simp_all only [ge_iff_le]
α : Type u_1
pre : Preorder α
dec : DecidableEq α
M N P : Multiset α
h : N ≤ M
this✝¹ : M - N + P + N = M - N + N + P
this✝ : M + P - N + N = M + P ∪ N
this : M + P ∪ N = M + P
⊢ M + P - N + N = M + P
no goals