## NATP

a recognizer for the natural numbers
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`

.