The logic of first order intuitionistic type theory with weak sigma-elimination
M. D. G. Swaen · Journal of Symbolic Logic · 1991
Abstract Via the formulas-as-types embedding certain extensions of Heyting Arithmetic can be represented in intuitionistic type theories. In this paper we discuss the embedding of ω-sorted Heyting Arithmetic HAω into a type theory WL, that can be described as Troelstra's system with so-called weak Σ-elimination rules. By syntactical means it is proved that a formula is derivable in HAω if and only if its corresponding type in WL is inhabited. Analogous results are proved for Diller's so-called restricted system and for a type theory based on predicate logic instead of arithmetic.