induction n with
| zero      =>
  rw [pow_zero, one_mul]
  exact sub_val_x_zero evr x
| succ n ih =>
  rwa [sub_val_val_pos_succ evr, pow_succ, mul_assoc, decr_val_p_mul]
R : Type u
inst✝¹ : CommRing R
inst✝ : IsDomain R
p : R
evr : ENatValRing p
x : R
n : ℕ
⊢ sub_val evr n (p ^ n * x) = x
no goals