Theorem: IMOSL.IMO2012A5.Case3.SCharNeTwo.ReductionLemmas.Lem3 (IMOSLLean4/IMO2012/A5/A5Cases/Case3.lean)

State before:
R : Type u_2
S : Type u_1
r : R
inst✝³ : Ring R
inst✝² : CharTwo R
inst✝¹ : Ring S
inst✝ : NoZeroDivisors S
hS : 2 ≠ 0
f : R → S
hf : NontrivialGood f
h : f r = -1
x : R
⊢ f (r * x + 1) = f (r + x) - f x
Tactic:
rw [hf.is_good, h, neg_one_mul, neg_add_eq_sub]
State after:
no goals