. simp;
  intro x y hwy hyx hx;
  existsi y;
  constructor;
  . simpa;
  . apply ih.mpr;
    existsi x;
    simp_all;
case succ.mpr
α : Type u_1
M : Model α
p q : Formula α
n : ℕ
ih : ∀ {w : M.World}, Satisfies M w (◇^[n]p) ↔ ∃ v, w ≺^[n] v ∧ Satisfies M v p
w : M.World
⊢ (∃ v, w ≺^[n + 1] v ∧ Satisfies M v p) → Satisfies M w (◇^[(n + 1)]p)
no goals