Description: Distribution of existential quantifiers, with a bound-variable hypothesis saying that y is not free in ph , but x can be free in ph (and there is no distinct variable condition on x and y ). Usage of this theorem is discouraged because it depends on ax-13 . Check out exdistr for a version requiring fewer axioms. (Contributed by Mario Carneiro, 20-Mar-2013) (Proof shortened by Wolf Lammen, 14-May-2018) (New usage is discouraged.)