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 | |- ( A. x x = y -> ph ) |
|
| Assertion | aecoms | |- ( A. y y = x -> ph ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | aecoms.1 | |- ( A. x x = y -> ph ) |
|
| 2 | aecom | |- ( A. y y = x <-> A. x x = y ) |
|
| 3 | 2 1 | sylbi | |- ( A. y y = x -> ph ) |