**numerals:**-
`0`and non-zero-initial strings of digits. Subsumed under constants for most purposes in this document; the main difference is that numerals are predeclared. **constants:**- Strings consisting of characters from the set
consisting of the letters (upper and lower case are allowed and
distinct), digits, and the characters
`_`and`?`. A numeral is not a constant, and a constant may not begin with`?`. Numerals are subsumed under constants in most respects, except that they are predeclared. **free variables:**- As constants, except that they begin with
`?`and should contain in addition some non-digit. **bound variables:**- A nonzero numeral prefixed with a
`?`is a bound variable.

Fri Sep 5 16:28:58 MDT 1997