PairRules.PEXISTS_IMP

STRUCTURE

LIBRARY

pair

SYNOPSIS

Moves a paired existential quantification inwards through an implication.

DESCRIPTION

When applied to a term of the form ?p. t ==> u, where variables from p are not free in both t and u, PEXISTS_IMP_CONV returns a theorem of one of three forms, depending on occurrences of variable from p in t and u. If variables from p are free in t but none are in u, then the theorem:

   |- (?p. t ==> u) = (!p. t) ==> u

is returned. If variables from p are free in u but none are in t, then the result is:

   |- (?p. t ==> u) = t ==> (?p. u)

And if no variable from p is free in either t nor u, then the result is:

   |- (?p. t ==> u) = (!p. t) ==> (?p. u)

FAILURE

PEXISTS_IMP_CONV fails if it is applied to a term not of the form ?p. t ==> u, or if it is applied to a term ?p. t ==> u in which the variables from p are free in both t and u.

SEEALSO

EXISTS_IMP_CONV, LEFT_IMP_PFORALL_CONV, RIGHT_IMP_PEXISTS_CONV