Module: Mathlib.LinearAlgebra.RootSystem.Finite.G2

Goal state before:
pp: ι : Type u_1
R : Type u_2
M : Type u_3
N : Type u_4
inst✝⁸ : CommRing R
inst✝⁷ : AddCommGroup M
inst✝⁶ : Module R M
inst✝⁵ : AddCommGroup N
inst✝⁴ : Module R N
P : RootPairing ι R M N
inst✝³ : P.EmbeddedG2
inst✝² : Finite ι
inst✝¹ : CharZero R
inst✝ : IsDomain R
i : ι
this : Fintype ι
B : P.InvariantForm
⊢ P.pairing i (threeShortAddLong P) * (B.form (P.root (threeShortAddLong P))) (P.root (threeShortAddLong P)) =
    (P.pairing i (short P) + P.pairing i (long P)) *
      (B.form (P.root (threeShortAddLong P))) (P.root (threeShortAddLong P))

Tactic:
calc P.pairing i (threeShortAddLong P) *
          B.form (threeShortAddLongRoot P) (threeShortAddLongRoot P)
    _ = 2 * B.form (P.root i) (threeShortAddLongRoot P) := ?_
    _ = 3 * (2 * B.form (P.root i) (shortRoot P)) + 2 * B.form (P.root i) (longRoot P) := ?_
    _ = P.pairing i (short P) * B.form (longRoot P) (longRoot P) +
          P.pairing i (long P) * B.form (longRoot P) (longRoot P) := ?_
    _ = (P.pairing i (short P) + P.pairing i (long P)) *
          B.form (threeShortAddLongRoot P) (threeShortAddLongRoot P) := ?_

Goal state after:
case calc_1
ι : Type u_1
R : Type u_2
M : Type u_3
N : Type u_4
inst✝⁸ : CommRing R
inst✝⁷ : AddCommGroup M
inst✝⁶ : Module R M
inst✝⁵ : AddCommGroup N
inst✝⁴ : Module R N
P : RootPairing ι R M N
inst✝³ : P.EmbeddedG2
inst✝² : Finite ι
inst✝¹ : CharZero R
inst✝ : IsDomain R
i : ι
this : Fintype ι
B : P.InvariantForm
⊢ P.pairing i (threeShortAddLong P) * (B.form (threeShortAddLongRoot P)) (threeShortAddLongRoot P) =
    2 * (B.form (P.root i)) (threeShortAddLongRoot P)

case calc_2
ι : Type u_1
R : Type u_2
M : Type u_3
N : Type u_4
inst✝⁸ : CommRing R
inst✝⁷ : AddCommGroup M
inst✝⁶ : Module R M
inst✝⁵ : AddCommGroup N
inst✝⁴ : Module R N
P : RootPairing ι R M N
inst✝³ : P.EmbeddedG2
inst✝² : Finite ι
inst✝¹ : CharZero R
inst✝ : IsDomain R
i : ι
this : Fintype ι
B : P.InvariantForm
⊢ 2 * (B.form (P.root i)) (threeShortAddLongRoot P) =
    3 * (2 * (B.form (P.root i)) (shortRoot P)) + 2 * (B.form (P.root i)) (longRoot P)

case calc_3
ι : Type u_1
R : Type u_2
M : Type u_3
N : Type u_4
inst✝⁸ : CommRing R
inst✝⁷ : AddCommGroup M
inst✝⁶ : Module R M
inst✝⁵ : AddCommGroup N
inst✝⁴ : Module R N
P : RootPairing ι R M N
inst✝³ : P.EmbeddedG2
inst✝² : Finite ι
inst✝¹ : CharZero R
inst✝ : IsDomain R
i : ι
this : Fintype ι
B : P.InvariantForm
⊢ 3 * (2 * (B.form (P.root i)) (shortRoot P)) + 2 * (B.form (P.root i)) (longRoot P) =
    P.pairing i (short P) * (B.form (longRoot P)) (longRoot P) +
      P.pairing i (long P) * (B.form (longRoot P)) (longRoot P)

case calc_4
ι : Type u_1
R : Type u_2
M : Type u_3
N : Type u_4
inst✝⁸ : CommRing R
inst✝⁷ : AddCommGroup M
inst✝⁶ : Module R M
inst✝⁵ : AddCommGroup N
inst✝⁴ : Module R N
P : RootPairing ι R M N
inst✝³ : P.EmbeddedG2
inst✝² : Finite ι
inst✝¹ : CharZero R
inst✝ : IsDomain R
i : ι
this : Fintype ι
B : P.InvariantForm
⊢ P.pairing i (short P) * (B.form (longRoot P)) (longRoot P) +
      P.pairing i (long P) * (B.form (longRoot P)) (longRoot P) =
    (P.pairing i (short P) + P.pairing i (long P)) * (B.form (threeShortAddLongRoot P)) (threeShortAddLongRoot P)