aesop
α : Type u
inst✝¹ : DecidableEq α
inst✝ : LT α
a a0 : α
M X : Multiset α
H✝ : a ::ₘ M = X + {a0}
hyp : ¬a = a0
a0_a : a0 ≠ a
b : α
H : Multiset.count a (a ::ₘ M) = Multiset.count a (X + {a0})
ba : b = a
this✝ : a ∈ X + {a0}
this : Multiset.count a (a ::ₘ M) = Multiset.count a M + 1
⊢ Multiset.count a (a0 ::ₘ X) = Multiset.count a (a0 ::ₘ X) - 1 + 1
no goals