∀ {M : Type u_4} {α : Type u_5} [inst : AddCommMonoid M] (f : SkewMonoidAlgebra M α) (a : α) (b : M)
  [inst_1 : DecidableEq α] [inst_2 : DecidableEq M],
  (f.update a b).support = if b = 0 then f.support.erase a else insert a f.support