English
IsOfFinOrder is defined as x having a finite order in a monoid: there exists n ≥ 1 with x^n = 1.
Русский
IsOfFinOrder определяется как существование конечного порядка: ∃ n ≥ 1: x^n = 1.
LaTeX
$$$\IsOfFinOrder(x) \equiv ∃ n \ge 1, x^n = 1$$$
Lean4
/-- `IsOfFinOrder` is a predicate on an element `x` of a monoid to be of finite order, i.e. there
exists `n ≥ 1` such that `x ^ n = 1`. -/
@[to_additive /-- `IsOfFinAddOrder` is a predicate on an element `a` of an
additive monoid to be of finite order, i.e. there exists `n ≥ 1` such that `n • a = 0`. -/
]
def IsOfFinOrder (x : G) : Prop :=
(1 : G) ∈ periodicPts (x * ·)