 … the argumentation of [Bishop 1967] looks very smooth and seems to follow directly from a certain conception of what sets, functions, etc. are, and we wish to discover a formalism which isolates the principles underlying this conception in the same way that Zermelo-Fraenkel set-theory isolates the principles underlying classical (nonconstructive) mathematics. We want these principles to be such as to make the process of formalization completely trivial, as it is in the classical case. (Myhill 1975: 347)