Constructing the Infimum of Two Projections

An elementary algorithm for computing the infimum of two projections in a Hilbert space is examined constructively. It is shown that in order to obtain a constructive convergence proof for the algorithm, one must add some hypotheses such as Markov's principle or the locatedness of a certain range; and that in the finite-dimensional case, the existence of both the infimum and the supremum of the two projections suffices for the convergence of the algorithm.