`GEN_PART_MATCH : (term -> term) -> thm -> term -> thm`

SYNOPSIS
Instantiates a theorem by matching part of it to a term.

DESCRIPTION
When applied to a `selector' function of type term -> term, a theorem and a term:
```   GEN_PART_MATCH fn (A |- !x1...xn. t) tm
```
the function GEN_PART_MATCH applies fn to t' (the result of specializing universally quantified variables in the conclusion of the theorem), and attempts to match the resulting term to the argument term tm. If it succeeds, the appropriately instantiated version of the theorem is returned. Limited higher-order matching is supported, and some attempt is made to maintain bound variable names in higher-order matching. Unlike PART_MATCH, free variables in the initial theorem that are unconstrained by the instantiation will be renamed if necessary to avoid clashes with determined free variables.

FAILURE CONDITIONS
Fails if the selector function fn fails when applied to the instantiated theorem, or if the match fails with the term it has provided.

EXAMPLE
See MATCH_MP_TAC for more basic examples. The following illustrates the difference with that function
```  # let th = ARITH_RULE `m = n ==> m + p = n + p`;;
val th : thm = |- m = n ==> m + p = n + p

# PART_MATCH lhand th `n:num = p`;;
val it : thm = |- n = p ==> n + p = p + p

# GEN_PART_MATCH lhand th `n:num = p`;;
val it : thm = |- n = p ==> n + p' = p + p'
```