English
The action by a group element g fixes the entire product: g • prodXSubSMul G R x = prodXSubSMul G R x.
Русский
Действие элемента группы g фиксирует произведение: g • prodXSubSMul G R x = prodXSubSMul G R x.
LaTeX
$$$g \cdot prodXSubSMul\ G\ R\ x = prodXSubSMul\ G\ R\ x$.$$
Lean4
theorem smul (x : R) (g : G) : g • prodXSubSMul G R x = prodXSubSMul G R x :=
letI := Classical.decEq R
Finset.smul_prod'.trans <|
Fintype.prod_bijective _ (MulAction.bijective g) _ _ fun g' ↦ by
rw [ofQuotientStabilizer_smul, smul_sub, Polynomial.smul_X, Polynomial.smul_C]