intro h f
case mpr
x : BoolExprNat
⊢ (∀ (f : Fin x.toBoolExpr.vars → Bool), BoolExpr.eval f x.toBoolExpr.attach = false) →
    ∀ (f : List Bool), eval f x = false
case mpr
x : BoolExprNat
h : ∀ (f : Fin x.toBoolExpr.vars → Bool), BoolExpr.eval f x.toBoolExpr.attach = false
f : List Bool
⊢ eval f x = false