Arithmetic negation function
Completion Axiom (completion-of-unary-minus):
(equal (unary-- x) (if (acl2-numberp x) (unary-- x) 0))
Guard for (unary-- x):
(acl2-numberp x)
Notice that like all arithmetic functions, unary-- treats non-numeric inputs as 0.
Calls of the macro - on one argument expand to calls of unary--; see -.
