Theorem equsb1

Description: Substitution applied to an atomic wff. Usage of this theorem is discouraged because it depends on ax-13 . Use the weaker equsb1v if possible. (Contributed by NM, 10-May-1993) (New usage is discouraged.)

	Ref	Expression
Assertion	equsb1	$$⊢\left[y/x\right]x=y$$

Proof

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