exfalso
case fls
ν : Type u_1
inst✝ : DecidableEq ν
x : ν
τ : PropAssignment ν
hτ : τ ⊨ fls
hτ' : ¬(PropAssignment.set τ x !τ x) ⊨ fls
⊢ x ∈ vars fls
case fls
ν : Type u_1
inst✝ : DecidableEq ν
x : ν
τ : PropAssignment ν
hτ : τ ⊨ fls
hτ' : ¬(PropAssignment.set τ x !τ x) ⊨ fls
⊢ False