LP, the Larch Prover -- Sample proof: useful kinds of axioms
The axioms in \dflink{set1.lp} fall into several categories:
- Induction rules
-
The first axiom, sort Set generated by {}, insert, asserts that all
elements of sort S can be obtained by finitely many applications of
insert to {}. It provides the basis for defintions and proofs by
induction.
- Explicit definitions
-
The second axiom, {e} = insert(e, {}), is a single \llink{formula} that
defines the operator {__} (as a constructor for a singleton set).
- Inductive definitions
-
The next two pairs of axioms provide induction definitions of the membership
operator \in and the subset operator \subseteq. Inductive definitions
generally consist of one formula per generator.
- Implicit definitions
-
The formula involving the union operator (\union), together with the other
axioms, completely constrains the interpretation of that operator.
- Constraining properties
-
The final axiom (that of the extensionality principle) expresses the fact that
if two sets have the same elements, then they must be the same set.