Proofs of non-deducibility in intuitionistic functional calculus
Andkzej Mostowski · Journal of Symbolic Logic · 1948
It has been proved by S. C. Kleene and David Nelson that the formula is intuitionistically non-deducible, i.e., non-deducible within the intuitionistic functional calculus. The aim of this note is to outline a general method which permits us to establish the intuitionistic non-deducibility of many formulas and in particular of the formula (1).