Recognizers of functions in terms.

In translated terms, the `functions' that are applied to argument terms are function symbols and lambda expressions.

The built-in predicates `pseudo-termp` and `termp`
recognize pseudo-terms and valid translated terms.
The following predicates recognize
lambda expressions in pseudo-terms and in valid translated terms,
as well as functions (in the sense above)
in pseudo-terms and in valid translated terms.

Note that the built-in predicate `symbolp` recognizes
functions in pseudo-terms that are not lambda expressions,
and that the predicate `function-symbolp` recognizes
functions in valid translated terms that are not lambda expressions
(the latter has guard `symbolp`,
so it must be actually preceded by a call of `symbolp`
in guard-verified code).
These predicates, with the ones below,
provide ways to recognize all kinds of functions in terms.

- Pseudo-termfnp
- Recognize pseudo-term-functions, i.e. functions in pseudo-terms.
- Pseudo-lambdap
- Recognize pseudo-lambda-expressions, i.e. lambda expressions in pseudo-terms.
- Lambdap
- Recognize valid translated lambda expression, i.e. lambda expressions in valid translated terms.
- Termfnp
- Recognize valid translated term functions, i.e. functions in valid translated terms.
- Pseudo-lambda-listp
- Recognize true lists of pseudo-lambda-expressions.
- Pseudo-termfn-listp
- Recognize true lists of pseudo-term-functions.
- Termfn-listp
- Recognize true lists of translated term functions.
- Lambda-listp
- Recognize true lists of translated lambda expressions.