Primitive Recursive Dependent Type Theory

We show that restricting the elimination principle of the natural numbers type in Martin-Löf Type Theory (MLTT) to a universe of types not containing Π-types ensures that all definable functions are primitive recursive. This extends the concept of primitive recursiveness to general types. We discuss extensions to univalent type theories and other notions of computability. We are inspired by earlier work by Martin Hofmann [19], work on Joyal's arithmetic universes [26], and Hugo Herbelin and Ludovic Patey's sketched Calculus of Primitive Recursive Constructions [17]

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We define a theory T pr that is a subtheory of MLTT with two universes U 0 : U 1 , such that all inductive types are finitary and U 0 is restricted to not contain Π-types: