A continuous, constructive solution to Hilbert's 17th problem. C.N. Delzell (1984) Inventiones mathematicae
A model for HAS. A topological interpretation of the theory of species of natural numbers Dirk van Dalen (1974) Fundamenta Mathematicae
A topological interpretation of second-order intuitionistic arithmetic Joan Rand Moschovakis (1973) Compositio Mathematica
An algebraic approach to the Heyting-Brouwer predicate calculus Cecylia Rauszer (1977) Fundamenta Mathematicae
Approximation theory of uniqueness conditions by existence conditions Nobuyoshi Motohashi (1984) Fundamenta Mathematicae