Drule.pp

A call to pp pos th finds the premise denoted by pos in th and promotes it so that it occurs as the outermost antecedent of the theorem. The theorem argument th is first normalised by a call to MP_CANON.

Any theorem whose top level operator (after universal quantifiers are stripped away) is an implication can be viewed as being of the form

   ∀v1 .. vn. p1 /\ p2 /\ .. pn ==> c

where the variables v1 to vn may be free in some of the antecedents and/or conclusion c. To promote a premise pi transforms the above into

   ∀va .. vk. pi ==> ∀vx .. vz. pa /\ pb ... /\ pj ==> c

The four constructors of the match_position type can be used to designate different premises. The Pos f form applies the function f to the list of premises, and is expected to return a member of the given list. The Pat q form finds the first premise that matches the given quotation pattern. In this context, Any is viewed as a synonym for Pos hd. Finally, the Concl form selects the conclusion of the theorem, and “promotes” it by taking the contrapositive of the theorem.

After promotion some cleanup is performed. If a contrapositive was taken, double negations in the promoted premise are removed, and in all cases, universal quantifiers of variables not present in the promoted premise are pushed down to govern other premises.