cases Y_in_ress <;> (subst_eqs; simp at * ; subst_eqs ; simp at *)
Y : TNode
y : Formula
y_in_Y :
  y ∈
    match Y with
    | (L, R, none) => ↑(L ++ R)
    | (L, R, some (Sum.inl (~'χ))) => ↑(L ++ R) + {~unload χ}
    | (L, R, some (Sum.inr (~'χ))) => ↑(L ++ R) + {~unload χ}
φ✝ ψ✝ : Formula
Y_in_ress : Y = ([], [~φ✝], none) ∨ Y = ([], [~ψ✝], none)
⊢ lmOfFormula y < 1 + (1 + lmOfFormula φ✝ + lmOfFormula ψ✝)
case inl.refl.refl
φ✝ ψ✝ : Formula
⊢ lmOfFormula φ✝ < 1 + lmOfFormula φ✝ + lmOfFormula ψ✝