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 | |- [ 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 |