Theorem 19.8a

Description: If a wff is true, it is true for at least one instance. Special case of Theorem 19.8 of Margaris p. 89. See 19.8v for a version with a disjoint variable condition requiring fewer axioms. (Contributed by NM, 9-Jan-1993) Allow a shortening of sp . (Revised by Wolf Lammen, 13-Jan-2018) (Proof shortened by Wolf Lammen, 8-Dec-2019)

	Ref	Expression
Assertion	19.8a	|- ( ph -> E. x ph )

Proof

Step	Hyp	Ref	Expression
1		ax12v	|- ( x = y -> ( ph -> A. x ( x = y -> ph ) ) )
2		alequexv	|- ( A. x ( x = y -> ph ) -> E. x ph )
3	1 2	syl6	|- ( x = y -> ( ph -> E. x ph ) )
4		ax6evr	|- E. y x = y
5	3 4	exlimiiv	|- ( ph -> E. x ph )