Abstract – Projects are generally undertaken because
they are part of the plans to meet business needs and charter
organizations to new levels of performance. Projects are
however constrained by conflicting demands and competing
priorities within the project environment. Neglecting to
manage these constraints accurately and effectively may be
sufficient to condemn a project even if all other project
management activities are performed to a high standard of
excellence. The aim of this paper is to improve the
interpretation of the triple constraint and its dynamics and
indicate how this may advance the delivery of project
success. An integrated model is proposed to facilitate the
strategic management of the triple constraint trade-offs as a
function of the project higher purpose.
Keywords - Project management, triple constraint,
trade-offs, scope, time, cost
Products and solutions need to be constructed faster,
cheaper and better. Around the world mission-critical
projects are being launched all the time involving
significant capital investments and high-risk ventures.
Projects are becoming the way of the working world.
What makes project delivery successful is however a topic
of much academic debate, and depends by whom and
against which value system the project is being evaluated.
It is generally agreed that to be considered successful, a
project must be fit for purpose (add strategic value) and it
must have achieved its delivery targets , .
In reality it is not always considered practical to
deliver all the project targets exactly as planned. Trade-
offs need to be considered and priorities must be set in
order to realize strategic decisions. The project
management body of knowledge (PMBOK®) endorses
that every project is governed by the triple constraint,
which reflects a framework for evaluating these
competing demands , , .
A. Introducing the triple constraint
The triple constraint is a critical project management
concept that originates from the basis for undertaking a
project and provides direction for framing the project. The
triple constraint constitutes one of the primary building
blocks of the project plan and is paramount to the
monitoring and controlling process group , , , ,
Although the triple constraint theme has various
interpretations, the literature shows a general agreement
that project scope, time and cost comprise the three key
triple constraint variables , , , , , , .
Project time addresses the scheduling and duration of the
project, cost addresses the budget and resources of the
project, and scope addresses the requirements and work of
the project. A time-constrained project is bounded by the
completion agenda, whereas a cost-constrained project is
bounded by the scheduling of expenditure. Scope-
constrained projects are bounded by the performance
criteria of the deliverables. Project quality constitutes an
integral dimension of project management and is
supported by the triple constraint , , , , ,
, , .
The project management triangle (Fig. 1) is a useful
model to illustrate the consequences of change on the
triple constraint to key project stakeholders. The triangle
reflects the fact that the three constraints are interrelated
and involve trade-offs – one side of the triangle cannot be
changed without impacting the others. Project quality
takes root in all three variables of the triple constraint and
is affected by balancing the three factors , .
It may easily be argued that triple constraint affairs
reside at the kernel of the most essential determinations
B. Introducing the research rationale
According to research by the Gartner Group, only
16% of information technology (IT) projects are
completed within the desired time frame and budget and
achieve the desired results. More than 30% of projects are
cancelled and over 50% of projects will experience cost
overruns. Less than 30% of the projects companies
employ to change their businesses are successful .
The current literature in the project management
domain suggests that there exists a lack of appropriate
(and consistent) scholarship on the triple constraint and its
dynamics . The term ‘triple constraint’ did not even
appear in the initial issues of the PMBOK® Guide
glossary or index.
Fig. 1. Project management triangle.
Theory of the Triple Constraint – a Conceptual Review
C. J. Van Wyngaard1, J. H. C. Pretorius2, L. Pretorius3
1Graduate Universities of Johannesburg and Pretoria, Employee Saab Electronic Defence Systems, South Africa
2Faculty of Engineering and the Built Environment, University of Johannesburg, Johannesburg, South Africa
3Graduate School of Technology Management, University of Pretoria, Pretoria, South Africa
978-1-4673-2945-3/12/$31.00 ©2012 IEEE 1991
This knowledge gap results in project managers not
being able to effectively prioritize and exploit the triple
constraint trade-offs. It is proposed that a thorough
comprehension of the triple constraint dynamics is
paramount to effective project management.
Another problem is that project managers often create
an illusion of tangible progress by relying heavily upon
traditional on-time, on-budget and on-target measures –
yet this tactic fails to address the strategy ambiguity or
establish appropriate project goals .
It has also become commonplace in many projects to
view the triple constraint trade-offs as organizational
problems that have a definitive solution (‘either/or’
choices) – yet this tactic fails to effectively negotiate the
triple constraint and leads to destructive conflict. Collins
& Porras discovered that instead of being oppressed by the
‘Tyranny of the Or’, highly visionary companies liberate
themselves with the ‘Genius of the And’ – the ability to
embrace both extremes of a number of dimensions at the
same time . This conjecture is supported by the
Polarity ManagementTM philosophy .
Without the effective management of the triple
constraint as an interrelated system, projects run the risk
of becoming separated from purpose. A mechanism is
needed on how to manage this seemingly contradictory
task when it comes to constraint trade-offs. The premise is
that if these constraints are managed properly,
organizations will be successful in delivering projects and
meeting organizational goals.
This paper examines the notion behind the project
management triangle and power structure of its
constraints. An integrated model is proposed for managing
relative flexibility within the triple constraint towards a
beneficial outcome in terms of project success.
II. RESEARCH METHODOLOGY
The basic structure of the research process used in the
study is presented in Fig. 2.
Qualitative review of theories
and literature related to the
research pro blem
Derive key a ttribute s to
formulate an integrated m odel
through conceptual analysis
Evaluate the integrated model
through case study exploration
Statement of the research
problem and hypoth esis
Design the research
methodology to investigate
the problem and to test the
Conclude on the
appropriatenes s of the
Fig. 2. Research process.
The type of study associated with this paper is
primarily non-empirical defined through an extensive
literature study, conceptual analysis and construction of an
integrated model using secondary data. Theory building in
the research occurred through retroductive and deductive
strategies. Conceptual explication was used to derive the
model through analysis and integration of concepts
discovered through the literature study.
The research undertook basic case study analysis as a
mechanism to demonstrate that the derived model is valid
and useful, which also introduced an empirical element
into the research design. The results from the case study
analysis have been generalized to refer back to the project
management body of knowledge in terms of applicability.
The integrated model presented in this paper is highly
conceptual. The emphasis in the study was on qualitative
reasoning both in definition, explanation and application,
rather than an emphasis on empirical and other
quantitative techniques. The findings of the research study
should thus be considered as preliminary rather than
conclusive, pending further research.
III. THEORETICAL FRAMEWORK
A substantial range of literature has been considered
in the study with reference to more than 100 sources
representing authoritative knowledge across the fields of
project management . This section provides an
overview of some of the key concepts surrounding the
triple constraint, and concludes with a consolidated triple
A. Dynamics of the triple constraint
The triple constraint continuously faces conflicting
demands and competing priorities within the project
milieu. For example, if the project is working to a fixed
level of scope then the cost of the project will largely be
dependent upon schedule availability. Similarly, when the
project time is fixed, the scope of the end product will
depend on the budget or resources available.
Project management researchers and authors widely
recognize that the inherent trade-off dynamics of the triple
constraint can be described by the following three key
relationships , , , :
S↑ α T↑ C↑ (1)
T↓ α S↓ C↑ (2)
C↓ α S↓ T↑, (3)
where the up-arrow (↑) implies an increase, the down-
arrow (↓) implies a decrease, and S, T, and C refers to
scope, time and cost respectively.
Relationships (1), (2) and (3) denote that any triple
constraint variable can be delivered at the expense of one
or both of the remaining two variables. Further analysis
signifies that when there is pressure on the triple
constraint, at least one of the variables needs to be flexible
in order to validate a quality balance , .
Proceedings of the 2012 IEEE IEEM
The dynamics of these relationships can be illustrated
in a variety of ways through manipulation of the project
management triangle. For example, if both the schedule
and budget of the project are negatively affected as a
result of an increase in project scope, the relationship may
be graphically illustrated as shown in Fig. 3.
Fig. 3 is only one of many possible ways of how to
illustrate these dynamic relationships. The illustrations
also depend on which factors are fixed and which are
flexible. It should be highlighted that the changes are not
always symmetric, i.e. if two variables need to increase,
one may increase proportionally more than the other – for
example, more resources may need to be added in order
not to exceed the deadline by too much.
The important consideration is that a connected
triangle must be maintained at all times. Fig. 4 illustrates
that it is not possible to maintain the triple constraint as a
triangle when all three variables are pursued
B. Good, fast, or cheap? Pick two
Within the project management and consulting
environment, the adage ‘good, fast or cheap - pick two’ is
commonly encountered. Good, fast and cheap respectively
refer to the three key elements of the triple constraint
namely the extent of work (scope), the schedule (time)
and the budget (cost). The notion is that projects are
generally constrained to choose two of the three elements
and sacrifice the other in order to gain the chosen two.
The ‘good, fast or cheap - pick two’ impression is a
manifestation of the ‘Tyranny of the Or’ – the rational
view that cannot easily accept paradox, that cannot live
with two seemingly contradictory forces or ideas at the
same time . This concept pushes people to believe that
things must be either A or B, but not both. That is to say,
in terms of the triple constraint, one can choose either
good-and-fast, or good-and-cheap, or fast-and-cheap; but
critically not all three (Fig. 4).
The ’good, fast or cheap - pick two’ trade-off can be
demonstrated with an adaptation of Barker & Cole’s
seesaw model as illustrated in Fig. 5. If pressure is put on
timescales (fast) then costs can be expected to go up;
alternatively, if pressure is put on costs (cheap) then
timescales can be expected to go up. From the seesaw
example it is clear that, with the scope of work (good)
remaining pivotal, the project cannot be delivered
simultaneously fast and cheap as well; one of the elements
has to be flexible , .
Fig. 3. The triple constraint relationship S↑ α T↑ C↑.
Fig. 4. Better, faster, cheaper – is this really possible?
The following analogy may be drawn between the
‘good, fast or cheap - pick two’ permutations and the key
triple constraint relationships :
1) Relationship 1, S↑ α T↑ C↑, implies that the
effect of increasing scope (S↑), or effort (pressure) to
achieve scope, necessitates an increase in time (T↑) and/or
cost (C↑). If cost remains unchanged, then the project can
be delivered good (because S↑) and cheap (because C
fixed as planned) but not fast (because T↑);
2) Relationship 2, T↓ α S↓ C↑, implies that the
effect of reducing time (T↓), or effort (pressure) to
achieve time, necessitates a reduction of scope (S↓) and/or
an increase in cost (C↑). If scope remains unchanged, then
the project can be delivered fast (because T↓) and good
(because S fixed as planned) but not cheap (because C↑);
3) Relationship 3, C↓ α S↓ T↑, implies that the
effect of reducing cost (C↓), or effort (pressure) to
achieve cost, necessitates a reduction of scope (S↓) and/or
an increase in time (T↑). If time remains unchanged, then
the project can be delivered cheap (because C↓) and fast
(because T fixed as planned) but not good (because S↓).
C. Supporting factors of the triple constraint
Within the context of this paper the three prime
elements of scope, time and cost are considered central to
the triple constraint. Project management literature,
however, sporadically indicates quality and performance
as an adjunct to or substitute for scope, and occasionally
designates customer satisfaction and project risk as
ancillary constraints .
Project scope encapsulates capability and grade
attributes. Quality and grade are not the same. Grade
refers to the set of attributes on which the quality of a
product will be judged . Quality constitutes an
uncompromising and inherent objective of the project
specification that takes root in all three properties of the
Fig. 5. Good-and-fast vs. good-and cheap.
Proceedings of the 2012 IEEE IEEM
A lower-grade material, for example, is not
necessarily a lower-quality material, as long as the grade
of material is appropriate for its intended use.
Performance is an operational assessment metric for the
triple constraint in terms of project accomplishment,
which should be continuously monitored and controlled
throughout the project. Performance and quality are hence
not substitutes for scope , , , .
Customer satisfaction is fulfillment of the consumer
requirements, expectations and needs, and constitutes a
performance measure in terms of quality or excellence.
Risk impacts the performance of the triple constraint,
which may precipitate change in terms of the triple
constraint trade-off dynamics , , , .
This paper presents a classic interpretation of the
triple constraint, focusing on the ‘big three’ of scope, time
and cost without adding or subdividing.
D. Power structure of the triple constraint
One of the challenges project managers face is the
iterative and infringing requirements of the customer. A
good starting point is thus to understand the customer’s
priorities in order to identify the most important aspect of
the project and obtain an optimum balance between the
constraints , .
Dobson’s theory on the Hierarchy of Constraints
defines a project by listing the triple constraint variables in
order of flexibility . Dobson proposes that exploitation
of flexibility in the weaker (more flexible) constraints can
be used as a tool to meet the absolute requirement of the
driver (least flexible) constraint in order for the project to
succeed. The driver constraint is derived from the raison
d’être of the project and is the constraint that has to be
met otherwise the project fails. There can only be one
project driver at any given time. The weak constraint has
the greatest flexibility, but is not necessarily the least
important. The middle constraint normally has a small
amount of flexibility and can either be very close to the
driver in importance to the project mission, or may
sometimes have flexibility more akin to the weak
It is important to note that flexibility, and not
importance, serves as the ranking criterion. Importance is
the relative merit of the constraints considering the long-
term value of the project. Flexibility is the extent to which
the project manager can manipulate the constraints in
order to successfully deliver the project .
It is presupposed that the effective management of the
triple constraint power structure and its dynamics is
central to project success. Details pertaining to trade-off
strategies and exploitation considerations are documented
E. Key attributes of the triple constraint
The following fundamental characteristics were
consolidated in support of the physiology of the
consolidated triple constraint model :
1) Effective projects bring form and function to
ideas or needs, and yield beneficial change or added value.
2) The higher purpose of a project is fundamentally
the driver of the project.
3) The triple constraint constitutes a balance of the
three interdependent project elements of scope, time and
cost as a function of the project higher purpose.
4) The concepts of quality, customer satisfaction,
performance and risk have an impact on the triple
constraint, but do not inherently constrain the project.
5) The cause and effect of new or changing triple
constraint requirements are constantly negotiated during
all phases of a project.
6) Change within the triple constraint is
compensated through proportional trade-offs.
7) Failure to deliver all three triple constraint
variables on target does not necessarily imply project
8) Flexibility is an indispensable triple constraint
requirement in order to accommodate shifts in project
emphasis, and to ensure a beneficial project outcome.
9) The three key triple constraint relationships
signify that at least one of the triple constraint variables
must be constrained (otherwise there is no baseline for
planning), and at least one of the variables must have
capacity for exploitation (otherwise quality may be
10) The triple constraint can be prioritized into a
power structure by ranking the variables into a hierarchy
of flexibility (capacity for exploitation).
11) The power structure derives from the project
objectives and higher purpose and may be influenced by
12) Capitalizing on the pliability of the two more
flexible constraints can be used as a mechanism to achieve
the essential demands of the primary triple constraint
variable (the driver).
F. Consolidated triple constraint model
The integrated model was realized through conceptual
synthesis of the key derived triple constraint attributes
discussed in the previous section. The matured model is
presented in Fig. 6. The consolidated model has been
dubbed the TRIJECT model (an acronym created from the
titles ‘TRIple constraint’ and ‘proJECT management’).
The project management triangle, which constitutes
the heart of the TRIJECT model, is supported by the two
more flexible constraints (time and cost in this instance)
and forms the foundation of the triangle. The primary
triple constraint variable (scope in this instance) aligns the
triangle with the project higher purpose. The triangle
projection is dynamic and can pivot about its axis to
accommodate change within its power structure. The
triple constraint hierarchy may be influenced by the
project environment, which impacts the higher purpose
and objectives of the project. The model embodies three
dimensions, in which each facet of the triple constraint
may drive the project.
Proceedings of the 2012 IEEE IEEM
Fig. 6. TRIJECT model.
The central presence of quality is signified by the
outline shape of the TRIJECT model, which, using some
imagination, resembles a capital letter ‘Q’.
The rationale of the TRIJECT model is based on the
achievement of the primary triple constraint variable
through the exploitation of the two more flexible
constraints and alignment with the project higher purpose.
The continuous cycle implied by the model represents
the ongoing and interrelated nature of this process as
change is introduced into the system. Monitoring and
controlling hence manifest a requisite part of this cycle.
The model also accounts for the ancillary issues such as
‘the why’ of the project and change within the project
environment as well as quality and control.
In practice the TRIJECT model is expected to overlap
and interact dynamically with the project management
process groups. Details pertaining to the proposed
protocol and application of the consolidated triple
constraint model are documented in .
IV. CASE STUDY ANALYSIS
Evaluation of the TRIJECT model was limited to the
exploratory review of the theoretical model and protocol
against a simplified case in order to facilitate a conceptual
understanding of the integrated model in practice. The
observed case was the building project of the Smithsonian
Institution, National Air and Space Museum (NASM) ,
. There is no claim that this case is representative of the
general project management milieu.
A. Case paraphrases and system definition
The NASM project mission, essentially, was to build
a world-class aviation and space museum for a budget of
approximately USD 40 million and open it on July 4,
1976. The project mission statement satisfies the triple
constraint, which is defined as follows:
1) Time constraint = July 4, 1976
2) Cost constraint = USD 40 million
3) Scope constraint = World-class museum.
A key part of the Smithsonian’s ability to get
congressional funding unlocked for the project involved
the national focus on the upcoming Bicentennial
celebrations. National attention would be focused on
Washington, D.C., and the National Mall during the
festivities, and the President of the United States would be
on hand to cut the ribbon. The consequences of missing
the Bicentennial would have been hugely humiliating for
the Smithsonian and for the NASM team. The time
constraint has therefore been assigned in the lead position
as the driver for this project. Before settling on the
primary triple constraint variable, the critical question of
why this project is being undertaken needs to be reviewed.
The term ‘world-class’ may constitute a variety of
potential meanings, each with different consequences for
time and cost. For example, how many air and spacecraft
should hang in the new building, or how complicated
should the audiovisual exhibits be. The distinction
between the work of the NASM and the project of the
NASM needs to be considered. The project ends, but the
work is ongoing. What must be done to meet the demands
of opening day is only a prelude to the indefinite lifespan
of the open museum. It can therefore be argued that the
scope constraint, although probably the most important, is
also the most flexible (weak) constraint for this project.
The USD 40 million federal appropriation is a definite
number, but not an exact one. Major construction projects
often have a contingency reserve of up to 10% of the
budget for change orders and other problems. Considering
flexibility and following the process of elimination, cost
may thus be identified as the middle constraint for this
B. Case investigation and system analysis
The triple constraint compromise to manage was
identified as the trade-off between the exploitation of the
USD 40 million budget (the cost constraint), and the
requirements / features that constitute a world-class
museum (the scope constraint). The success of this project
was driven by the deadline (the time constraint) to open
the museum on the nation’s Bicentennial celebration July
4, 1976 in order to attain national focus (the higher
purpose). With the project mission and triple constraint
power structure defined, the TRIJECT model for the
NASM project can be delineated as shown in Fig. 7.
Exploitation of the project budget (C↑) alleviates the
pressure to rollback on the museum’s scope requirements,
and supplements the effort to ensure that the deadline for
opening the museum is met (more money and resources
can be spent to get the same or more work accomplished
within a limited period of time). The cost constraint
includes both cash and non-cash resources. Exploitation of
the project scope (S↓), on the other hand, alleviates the
pressure to add additional cost and resources to the
museum budget, but also supplements the effort to ensure
that the deadline for opening the museum is met.
Exploiting flexibility in the scope constraint should
however not compromise quality, i.e. the museum’s
Proceedings of the 2012 IEEE IEEM
world-class criteria, which Congress values. One
mechanism for exploiting the scope of the museum
building program is to downsize selected objectives and
quality metrics that do not add customer value.
Because it was simpler to exploit the ‘world-class’
scope requirements than it was to exploit the
congressional budget, the system was initially located in
the right half of Fig. 8, i.e. the flexibility of project scope
outweighed the flexibility of project cost. The kinetics of
Fig. 8 constitute a reverse congruency with respect to Fig.
5, focusing on exploitation causality rather than on
constraints. The risk for the NASM case is that excessive
manipulation of the scope requirements may eventually
result in the benefits of this effort to disperse as the system
moves into its downside (R-). This may put the project at
risk to not deliver a world-class aviation and space
museum, with inadequate artifacts and exhibits. As these
disadvantages are being experienced, an increasing
awareness may develop towards the advantages of budget
exploitation (L+). This awareness may shift the focus of
manipulation by sliding the exploitation weight up the
seesaw from R- to L+. Accordingly, excessive
manipulation of the budget requirements may again
transition the system into its downside (L-). The
consequent risk is that the project may be completed
substantially over budget, and the project schedule may
also be expected to slip due to the restoration of additional
artifacts and the incorporation of complex exhibits. What
is called for is a dynamic mechanism that may equilibrate
the system as exploitation weight shifts and trade-offs are
compromised during the project.
C. Case discussion and system guidelines
In order to effectively manage the exploitation trade-
off, the project manager needs to consider each of the
benefits in the upper quadrants and define how to gain or
maintain these advantages. A risk strategy is also required.
The flexibility in the weaker constraints is not unlimited
since there is always a minimum that must be achieved.
The project manager needs to consider each of the
disadvantages in the lower quadrants and define indicators
that will alert the project team when the project dips into
the red zone of over focusing the exploitation effort.
Fig. 7. TRIJECT model for the NASM case.
Fig. 8. System diagnosis of the NASM case .
The following considerations have been identified for
obtaining and sustaining the positive results of the L+
quadrant of the NASM case: Find out what degree of
budget overrun will be acceptable; Find out if contingency
funds are available; Investigate if additional staff and
equipment can be borrowed; Determine which costs will
not be charged to the project; Establish how political
influence can be achieved in order to pursue budget
flexibility; Examine the consequences that the various
interpretations of the ‘world-class’ requirement may have
on the project; Identify the air and spacecraft which posses
overwhelming historical significance; Discern how time
and cost of artifact restorations can be optimized;
Determine the appropriate requirement and level of
complexity for the museum’s audiovisual exhibits; Take
the law of diminishing returns into consideration.
Retrospectively, the considerations to obtain and
sustain the positive results of the R+ quadrant include:
Establish effective and proven practices to efficiently
manage and control the project budget; Identify those
aspects of the project scope requirements that are not
quality related; Target areas for exploitation where scope
creep is detected; Reach a common understanding with
the stakeholders on the importance they place on the
delivery of each scope requirement, and ascertain the
could-have’s and would-have’s; Ensure that the ‘world-
class’ criterion is not dismissed due to excessive artifact
and exhibit cutbacks; Investigate where initial objectives
may be downsized, for example lowering the planned
number of air and spacecraft for opening day; Determine
quality metrics that do not add customer value, for
example trimming back on complicated audiovisual
The following red zone indicators (early warnings)
have been identified for when the project falls in the L-
quadrant of the NASM case: Resistance from Congress
regarding the increased project cost; Spending additional
money and resources have reached the point where it no
longer adds value to the project schedule, i.e. recognizing
the law of diminishing returns; Artifact restorations and
audiovisual exhibits fall behind schedule. The red zone
indicators for when the project falls in the R- quadrant
include: The ‘world-class’ requirement of the museum
comes into question; Criticism regarding the
appropriateness of artifacts and degree of exhibits.
The project team needs to monitor these dynamics
within the triple constraint power structure throughout the
project life cycle. The timely identification of divergences
Proceedings of the 2012 IEEE IEEM
from the project higher purpose followed by the
appropriate corrective actions is crucial.
The NASM project might have benefited more by
sustaining the positive results of both upper quadrants
(green zone) and minimizing the time spent in the lower
quadrants (red zone) – thus, delivering the project fast as
well as relatively good and cheap (Fig. 9). A possible
solution that effectively addresses this challenge is
proposed in .
The study of the triple constraint is believed to be one
of the most overlooked fundamentals of project
management. As a result of the various perspectives and
interpretations across literature that surround the project
management triangle and triple constraint, the need for a
unified model has been identified. The TRIJECT model
supports an understanding of finite resources and
facilitates a mechanism for managing the competing triple
constraint requirements. The model encourages the
creative exploitation of the triple constraint to improve
project performance by considering the relative flexibility
between the key elements. The goal of the model is to
maintain the focus of the triple constraint power structure
on the project higher purpose.
The case study presented has demonstrated that the
integrated model may furnish the instruments that enable
project teams to manage their work in line with the
absolute requirements for project success. It should be
taken in consideration that every project will experience
its own unique limitations to exploitation capacity, which
needs to be assessed through appropriate ‘cost’ vs. value
impact analyses. Projects should however aim to always
deliver to a much greater extent in terms of value than the
sacrifice of the exploitation effort.
An integrated framework is suggested in , which
evolves the strategic management of the TRIJECT model
using Polarity ManagementTM techniques. Supporting
quantitative studies may be justified to conclude the real
world pertinence of these conceptual models.
The support for research collaboration by the National
Research Foundation (NRF) in South Africa is
Fig. 9. Effective management of the NASM case .
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