English
If an equivalence maps x to a central element, then its image remains central.
Русский
Если отображение из класса эквивалентности переводит элемент x в центральный элемент, то его образ остаётся центральным.
LaTeX
$$∀ e, x ∈ center M, e x ∈ center N$$
Lean4
/-- The center of a multiplication with unit is commutative and associative.
This is not an instance as it forms an non-defeq diamond with `Submonoid.toMonoid` in the `npow`
field. -/
@[to_additive /-- The center of an addition with zero is commutative and associative. -/
]
abbrev commMonoid' : CommMonoid (center M) :=
{ (center M).toMulOneClass, Subsemigroup.center.commSemigroup with }