Some remarks on blvarlational bounds and the pointwise estimation of solutions

When a given equation can be realised in some Hilbert space H as an operator equation in the from Ad] then it is known that complementary variational bounds can be obtained for the inner product d]. Recently it has been shown that complementary bivariational bounds can be obtained for the inner product d]associated with the equation Ad]= f and an arbitary elementy d]. These latter bounds are a natural starting point for investigatng pointwise estimatesd of solutions provided thta certain questions relating, on the one hand, to the self-adjointness and the invertibility of associated operators and on the other to the availability of a suitable large Hilbert space can be resolved. We show that if the underlying problem can be given an operator realisation in a suitably equipped Hilbert space then pointwise estimates of solution can be obtained