-- Mathlib/GroupTheory/Exponent.lean
/-- If two commuting elements `x` and `y` of a monoid have order `n` and `m`, there is an element
of order `lcm n m`. The result actually gives an explicit (computable) element, written as the
product of a power of `x` and a power of `y`. See also the result below if you don't need the
explicit formula. -/
@[to_additive "If two commuting elements `x` and `y` of an additive monoid have order `n` and `m`,
there is an element of order `lcm n m`. The result actually gives an explicit (computable) element,
written as the sum of a multiple of `x` and a multiple of `y`. See also the result below if you
don't need the explicit formula."]
lemma _root_.Commute.orderOf_mul_pow_eq_lcm {x y : G} (h : Commute x y) (hx : orderOf x ≠ 0)
    (hy : orderOf y ≠ 0) :
    orderOf (x ^ (orderOf x / (factorizationLCMLeft (orderOf x) (orderOf y))) *
      y ^ (orderOf y / factorizationLCMRight (orderOf x) (orderOf y))) =
      Nat.lcm (orderOf x) (orderOf y)

Proof state:
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ (orderOf (x ^ (orderOf x / (orderOf x).factorizationLCMLeft (orderOf y)))).Coprime
    (orderOf (y ^ (orderOf y / (orderOf x).factorizationLCMRight (orderOf y))))

Tactic:
iterate 2 rw [orderOf_pow_orderOf_div]; try rw [Coprime]

Result:
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ ((orderOf x).factorizationLCMLeft (orderOf y)).gcd ((orderOf x).factorizationLCMRight (orderOf y)) = 1

case hx
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ orderOf y ≠ 0

case hn
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ (orderOf x).factorizationLCMRight (orderOf y) ∣ orderOf y

case hx
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ orderOf x ≠ 0

case hn
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ (orderOf x).factorizationLCMLeft (orderOf y) ∣ orderOf x

Proof state:
case hn
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ (orderOf x).factorizationLCMLeft (orderOf y) ∣ orderOf x

Tactic:
simp [factorizationLCMLeft_mul_factorizationLCMRight, factorizationLCMLeft_dvd_left,
factorizationLCMRight_dvd_right, coprime_factorizationLCMLeft_factorizationLCMRight, hx, hy]

Result:
no goals

Proof state:
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ (orderOf x).factorizationLCMLeft (orderOf y) * (orderOf x).factorizationLCMRight (orderOf y) =
    (orderOf x).lcm (orderOf y)

case hx
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ orderOf y ≠ 0

case hn
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ (orderOf x).factorizationLCMRight (orderOf y) ∣ orderOf y

case hx
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ orderOf x ≠ 0

case hn
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ (orderOf x).factorizationLCMLeft (orderOf y) ∣ orderOf x

G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ ((orderOf x).factorizationLCMLeft (orderOf y)).gcd ((orderOf x).factorizationLCMRight (orderOf y)) = 1

case hx
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ orderOf y ≠ 0

case hn
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ (orderOf x).factorizationLCMRight (orderOf y) ∣ orderOf y

case hx
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ orderOf x ≠ 0

case hn
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ (orderOf x).factorizationLCMLeft (orderOf y) ∣ orderOf x

Tactic:
all_goals simp [factorizationLCMLeft_mul_factorizationLCMRight, factorizationLCMLeft_dvd_left,
  factorizationLCMRight_dvd_right, coprime_factorizationLCMLeft_factorizationLCMRight, hx, hy]

Result:
no goals

Proof state:
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ orderOf (x ^ (orderOf x / (orderOf x).factorizationLCMLeft (orderOf y))) *
      orderOf (y ^ (orderOf y / (orderOf x).factorizationLCMRight (orderOf y))) =
    (orderOf x).lcm (orderOf y)

G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ (orderOf (x ^ (orderOf x / (orderOf x).factorizationLCMLeft (orderOf y)))).Coprime
    (orderOf (y ^ (orderOf y / (orderOf x).factorizationLCMRight (orderOf y))))

Tactic:
all_goals iterate 2 rw [orderOf_pow_orderOf_div]; try rw [Coprime]

Result:
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ (orderOf x).factorizationLCMLeft (orderOf y) * (orderOf x).factorizationLCMRight (orderOf y) =
    (orderOf x).lcm (orderOf y)

case hx
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ orderOf y ≠ 0

case hn
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ (orderOf x).factorizationLCMRight (orderOf y) ∣ orderOf y

case hx
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ orderOf x ≠ 0

case hn
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ (orderOf x).factorizationLCMLeft (orderOf y) ∣ orderOf x

G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ ((orderOf x).factorizationLCMLeft (orderOf y)).gcd ((orderOf x).factorizationLCMRight (orderOf y)) = 1

case hx
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ orderOf y ≠ 0

case hn
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ (orderOf x).factorizationLCMRight (orderOf y) ∣ orderOf y

case hx
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ orderOf x ≠ 0

case hn
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ (orderOf x).factorizationLCMLeft (orderOf y) ∣ orderOf x

Proof state:
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ orderOf
      (x ^ (orderOf x / (orderOf x).factorizationLCMLeft (orderOf y)) *
        y ^ (orderOf y / (orderOf x).factorizationLCMRight (orderOf y))) =
    (orderOf x).lcm (orderOf y)

Tactic:
rw [(h.pow_pow _ _).orderOf_mul_eq_mul_orderOf_of_coprime]

Result:
G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ orderOf (x ^ (orderOf x / (orderOf x).factorizationLCMLeft (orderOf y))) *
      orderOf (y ^ (orderOf y / (orderOf x).factorizationLCMRight (orderOf y))) =
    (orderOf x).lcm (orderOf y)

G : Type u
inst✝ : Monoid G
x y : G
h : Commute x y
hx : orderOf x ≠ 0
hy : orderOf y ≠ 0
⊢ (orderOf (x ^ (orderOf x / (orderOf x).factorizationLCMLeft (orderOf y)))).Coprime
    (orderOf (y ^ (orderOf y / (orderOf x).factorizationLCMRight (orderOf y))))