Theorem equsb2

Description: Substitution applied to an atomic wff. Usage of this theorem is discouraged because it depends on ax-13 . Check out equsb1v for a version requiring less axioms. (Contributed by NM, 10-May-1993) (New usage is discouraged.)

	Ref	Expression
Assertion	equsb2	$$⊢\left[y/x\right]y=x$$

Proof

Step	Hyp	Ref	Expression
1		sb2	$$⊢\forall x\left(x=y\to y=x\right)\to \left[y/x\right]y=x$$
2		equcomi	$$⊢x=y\to y=x$$
3	1 2	mpg	$$⊢\left[y/x\right]y=x$$