prove_constructors_distinct

`prove_constructors_distinct`

Prim_rec.prove_constructors_distinct : (thm -> thm)

Proves that the constructors of an automatically-defined concrete type yield distinct values.

prove_constructors_distinct takes as its argument a primitive recursion theorem, in the form returned by define_type for an automatically-defined concrete type. When applied to such a theorem, prove_constructors_distinct automatically proves and returns a theorem which states that distinct constructors of the concrete type in question yield distinct values of this type.

Failure

Fails if the argument is not a theorem of the form returned by define_type, or if the concrete type in question has only one constructor.

Example

Given the following primitive recursion theorem for labelled binary trees:

   |- !f0 f1.
        ?! fn.
        (!x. fn(LEAF x) = f0 x) /\
        (!b1 b2. fn(NODE b1 b2) = f1(fn b1)(fn b2)b1 b2)

prove_constructors_distinct proves and returns the theorem:

   |- !x b1 b2. ~(LEAF x = NODE b1 b2)

This states that leaf nodes are different from internal nodes. When the concrete type in question has more than two constructors, the resulting theorem is just conjunction of inequalities of this kind.

HOL: Reference