norm_num
α : Type u_1
inst✝¹ : CommGroup α
inst✝ : DecidableEq α
s✝ s' t✝ t' C✝ : Finset α
a✝ b a : α
s t C : Finset α
has : a ∈ s
hst : (s ∩ a • C.mulStab * (t ∩ a • C.mulStab)).mulStab ⊆ C.mulStab
hC : C.Nonempty
⊢ ↑C.mulStab.card - ↑(s ∩ a • C.mulStab * (s ∩ a • C.mulStab * (t ∩ a • C.mulStab)).mulStab).card -
        ↑(t ∩ a • C.mulStab * (s ∩ a • C.mulStab * (t ∩ a • C.mulStab)).mulStab).card +
      ↑((s ∩ a • C.mulStab * (s ∩ a • C.mulStab * (t ∩ a • C.mulStab)).mulStab).card +
          (t ∩ a • C.mulStab * (s ∩ a • C.mulStab * (t ∩ a • C.mulStab)).mulStab).card) ≤
    ↑C.mulStab.card
no goals