no goals
R : Type u_1
inst✝ : Semiring R
k m n : ℕ
u v w : R
hkm : k < m
hmn : m < n
⊢ coeff (trinomial k m n u v w) m = v
rw [trinomial_def, coeff_add, coeff_add, coeff_C_mul_X_pow, coeff_C_mul_X_pow, coeff_C_mul_X_pow,
  if_neg hkm.ne', if_pos rfl, if_neg hmn.ne, zero_add, add_zero]