[SCL] SCL spec

[Chris Menzel]

I've put an SCL spec on the web: http://cl.tamu.edu/docs/scl.html .
It is not highly polished, but it will do as a start to get ideas fixed.

Features (all negotiable):

* No distinction between predicates and individual constants.
* Hence, no syntactic notion of arity (though arity could be enforced
  axiomatically for any given constant).
* Semantically there is a distinction between individuals and relations,
  but nothing prevents the class of relations from overlapping or being
  included in the class of individuals.
* Relations do not come with fixed arities (though of course nothing
  prevents introducing such relations).
* There is a separate class of function symbols.
* Function symbols are variably polyadic.
* Sequence variables can only occur in tail position in function terms
  and atomic formulas.
* Sequence variables never explicitly quantified; semantically, they are 
  implicitly universally quantified by quantifiers with widest possible
  scope.

Comments/criticism/discussion/correction welcome.

-chris