GSYM

Conv.GSYM : thm -> thm

Reverses the first equation(s) encountered in a top-down search.

The inference rule GSYM reverses the first equation(s) encountered in a top-down search of the conclusion of the argument theorem. An equation will be reversed iff it is not a proper subterm of another equation. If a theorem contains no equations, it will be returned unchanged.

    A |- ..(s1 = s2)...(t1 = t2)..
   --------------------------------  GSYM
    A |- ..(s2 = s1)...(t2 = t1)..

Failure

Never fails, and never loops infinitely.

Example

> arithmeticTheory.ADD;
val it = ⊢ (∀n. 0 + n = n) ∧ ∀m n. SUC m + n = SUC (m + n): thm

> GSYM arithmeticTheory.ADD;
val it = ⊢ (∀n. n = 0 + n) ∧ ∀m n. SUC (m + n) = SUC m + n: thm

See also

Drule.NOT_EQ_SYM, Thm.REFL, Thm.SYM