Major Section: PROGRAMMING
The natural numbers is the set of all non-negative integers,
{0,1,2,3,...}. Natp returns t if and only its argument is a
natural number, and nil otherwise. We recommend the file
books/arithmetic/natp-posp.lisp as a book for reasoning about posp
and natp. This book is included in books/arithmetic/top and
books/arithmetic/top-with-meta.