Theorem aecoms

Description: A commutation rule for identical variable specifiers. Usage of this theorem is discouraged because it depends on ax-13 . (Contributed by NM, 10-May-1993) (New usage is discouraged.)

	Ref	Expression
Hypothesis	aecoms.1	$$⊢\forall xx=y\to \phi$$
Assertion	aecoms	$$⊢\forall yy=x\to \phi$$

Proof

Step	Hyp	Ref	Expression
1		aecoms.1	$$⊢\forall xx=y\to \phi$$
2		aecom	$$⊢\forall yy=x\leftrightarrow \forall xx=y$$
3	2 1	sylbi	$$⊢\forall yy=x\to \phi$$