left
case pos
l₁ l₂ : ILit
hlit : toVar l₁ = toVar l₂
hpol : polarity l₁ = polarity l₂
⊢ l₁ = l₂ ∨ negate l₁ = l₂
case pos.h
l₁ l₂ : ILit
hlit : toVar l₁ = toVar l₂
hpol : polarity l₁ = polarity l₂
⊢ l₁ = l₂