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 fewer axioms. (Contributed by NM, 10-May-1993) (New usage is discouraged.)
Ref | Expression | ||
---|---|---|---|
Assertion | equsb2 | |- [ y / x ] y = x |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | sb2 | |- ( A. x ( x = y -> y = x ) -> [ y / x ] y = x ) |
|
2 | equcomi | |- ( x = y -> y = x ) |
|
3 | 1 2 | mpg | |- [ y / x ] y = x |