English
There is a natural action of M on the elements of the orbit of a, induced from the action on α.
Русский
Существует естественное действие M на элементы орбиты a, наследуемое от действия на α.
LaTeX
$$$\text{MulAction}_{M}(\operatorname{orbit}(M,a).\text{Elem})$ is well-defined with smul defined by restrictions.$$
Lean4
@[to_additive]
instance {a : α} : MulAction M (orbit M a)
where
smul m := (mapsTo_smul_orbit m a).restrict _ _ _
one_smul m := Subtype.ext (one_smul M (m : α))
mul_smul m m' a' := Subtype.ext (mul_smul m m' (a' : α))