case conv_symm h2_phi h2_phi' _ h2_ih =>
  symm
  exact h2_ih V
D : Type
I : Interpretation D
M : MetaValuation D
E : Env
F F' : Formula
h1 : E.WellFormed
h2_phi h2_phi' : Formula
a✝ : IsConv E h2_phi h2_phi'
h2_ih : ∀ (V : Valuation D), Holds D I V M E h2_phi ↔ Holds D I V M E h2_phi'
V : Valuation D
⊢ Holds D I V M E h2_phi' ↔ Holds D I V M E h2_phi
no goals