Theorem: ClassicalPropositionalLogic.isTrue_equiv (GlimpseOfLean/Exercises/Topics/ClassicalPropositionalLogic.lean)

State before:
v : Variable → Prop
A B : Formula
⊢ IsTrue v (A ⇔ B) ↔ (IsTrue v A ↔ IsTrue v B)
Tactic:
sorry
State after:
no goals