rw [hf, self_eq_add_right] at hsum'
case intro.refine_3
n d : ℕ
inst✝ : NeZero d
w : Weight n d
hE : E (trunc w) = E w
k : Fin (Nat.succ n)
hk : w k = 0
w' : Weight n d := Function.update (trunc w) k 1
j : Fin (Nat.succ n)
hj : E w < w j
hsum' : Weight.sum w' = Weight.sum (trunc w) + 1
hE' : E w' = E (trunc w)
hf : trunc w = w'
⊢ False
case intro.refine_3
n d : ℕ
inst✝ : NeZero d
w : Weight n d
hE : E (trunc w) = E w
k : Fin (Nat.succ n)
hk : w k = 0
w' : Weight n d := Function.update (trunc w) k 1
j : Fin (Nat.succ n)
hj : E w < w j
hsum' : 1 = 0
hE' : E w' = E (trunc w)
hf : trunc w = w'
⊢ False