Learning note 7/15

1. Term algebra provides us an algebraic formalization on the term signature, so that
we can use tool from algebra to study term. So in a sense, Herbrand is a smart guy.

2. The only identities or equational classes in term algebra are those syntatical identities.

3. It is(is it?) possible to have a sigma-algebras which has it's own equational classes that can not be formalized by the identities in sigma-signature.

4. A spec=<\sigma,E> is only a form of algebraic specification, we can replace E by
a bunch of axioms.