Complexity of morphism-based CG operations (maximal join, unification, subsumption, generalization) has been identified and studied by several authors. As a consequence, compromise have been proposed, either by assuming a restricted form of CG or by defining a simple or inefficient CG operation. Independently from this approach, this paper proposes to start a CG operation (like maximal join, ... [Show full abstract] unify and projection) by a bootstrap step. The bootstrap step is supplied by any information that specifies which concepts in the first CG should be mapped to corresponding concepts in the second CG. Three sources of information for the bootstrap are identified in this paper : a) entry concepts that are given to a CG operation, b) concepts with individual or set as referent and c) co-references that are used in compound CGs.