Abstract

We describe a non-constructive extension to Primitive Recursive Arithmetic, both abstractly, and as implemented on the Boyer-Moore prover. Abstractly, this extension is obtained by adding the unbounded ¯ operator applied to primitive recursive functions; doing so, one can define the Ackermann function and prove the consistency of Primitive Recursive Arithmetic. The implementation does not mention the ¯ operator explicitly, but has the strength to define the ¯ operator through the built-in functions EVAL$ and V&C$. x1. INTRODUCTION This paper is a mixture of theory and practice. The theory begins with the notions of constructivism and finitism in the philosophy of mathematics. As with all philosophical notions, these cannot appear directly in a mathematical theorem or a computer program, but they have been useful guides over the past hundred years to discovering mathematical results, and more recently, to designing computer implementations. Informally, a constructivist only believes in...

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