When applied to a ‘selector’ function of type term -> term, a theorem and a
term:
PART_MATCH fn (A |- !p1...pn. t) tm
the function PART_PMATCH applies fn to t' (the result
of specializing universally quantified pairs 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.