... have different signs. Without any loss of generality, we assume that h1 (a, b, c, d) < h 2 (a, b, c, d), then (4.7) is satisfied for all t k ∈ (h 1 (a, b, c, d), h 2 (a, b, c, d)). Hence, if the stepsize is taken in the interval (0, h 2 (a, b, c, d)), then the stability of the scheme will be guaranteed.If A(a, b,c, d) = 0, then B(a, b, c, d) = b 2a 2 and by Theorem 4.5, b 2 < a 2 , and so B(a, b, c, d) < 0. In this case, for all stepsizes, relation (4.7) is satisfied, and so unconditional stability arises. ...