∀ {R : Type u_1} [inst : Semiring R] {m : Type u_2} {n : Type u_3} [inst_1 : Fintype m] [inst_2 : DecidableEq m]
  (M : Matrix m n R), (fun f i j => f ((LinearMap.single R (fun x => R) i) 1) j) M.vecMulLinear = M