Theorem: Polynomial.natDegree_cancelLeads_lt_of_natDegree_le_natDegree_of_comm
File: Mathlib/Algebra/Polynomial/CancelLeads.lean

tactic: by_cases hp : p = 0
state_before: R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
⊢ (p.cancelLeads q).natDegree < q.natDegree
state_after: case pos
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : p = 0
⊢ (p.cancelLeads q).natDegree < q.natDegree

case neg
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
⊢ (p.cancelLeads q).natDegree < q.natDegree

tactic: rw [cancelLeads, sub_eq_add_neg, tsub_eq_zero_iff_le.mpr h, pow_zero, mul_one]
state_before: case neg
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
⊢ (p.cancelLeads q).natDegree < q.natDegree
state_after: case neg
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
⊢ (C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p)).natDegree < q.natDegree

tactic: by_cases h0 :
  C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p) = 0
state_before: case neg
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
⊢ (C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p)).natDegree < q.natDegree
state_after: case pos
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
h0 : C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p) = 0
⊢ (C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p)).natDegree < q.natDegree

case neg
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
h0 : ¬C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p) = 0
⊢ (C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p)).natDegree < q.natDegree

tactic: apply lt_of_le_of_ne
state_before: case neg
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
h0 : ¬C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p) = 0
⊢ (C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p)).natDegree < q.natDegree
state_after: case neg.a
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
h0 : ¬C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p) = 0
⊢ (C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p)).natDegree ≤ q.natDegree

case neg.a
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
h0 : ¬C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p) = 0
⊢ (C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p)).natDegree ≠ q.natDegree

tactic: convert hq
state_before: case pos
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : p = 0
⊢ (p.cancelLeads q).natDegree < q.natDegree
state_after: case h.e'_3
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : p = 0
⊢ (p.cancelLeads q).natDegree = 0

tactic: simp [hp, cancelLeads]
state_before: case h.e'_3
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : p = 0
⊢ (p.cancelLeads q).natDegree = 0
state_after: no goals

tactic: exact (le_of_eq (by simp only [h0, natDegree_zero])).trans_lt hq
state_before: case pos
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
h0 : C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p) = 0
⊢ (C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p)).natDegree < q.natDegree
state_after: no goals

tactic: simp only [h0, natDegree_zero]
state_before: R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
h0 : C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p) = 0
⊢ (C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p)).natDegree = 0
state_after: no goals

tactic: compute_degree!
state_before: case neg.a
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
h0 : ¬C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p) = 0
⊢ (C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p)).natDegree ≤ q.natDegree
state_after: case neg.a.a
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
h0 : ¬C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p) = 0
⊢ q.natDegree - p.natDegree + p.natDegree ≤ q.natDegree

tactic: rwa [Nat.sub_add_cancel]
state_before: case neg.a.a
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
h0 : ¬C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p) = 0
⊢ q.natDegree - p.natDegree + p.natDegree ≤ q.natDegree
state_after: no goals

tactic: contrapose! h0
state_before: case neg.a
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
h0 : ¬C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p) = 0
⊢ (C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p)).natDegree ≠ q.natDegree
state_after: case neg.a
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
h0 : (C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p)).natDegree = q.natDegree
⊢ C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p) = 0

tactic: rw [← leadingCoeff_eq_zero, leadingCoeff, h0, mul_assoc, X_pow_mul, ← tsub_add_cancel_of_le h,
  add_comm _ p.natDegree]
state_before: case neg.a
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
h0 : (C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p)).natDegree = q.natDegree
⊢ C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p) = 0
state_after: case neg.a
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
h0 : (C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p)).natDegree = q.natDegree
⊢ (C p.leadingCoeff * q +
          -(C q.leadingCoeff * (p * X ^ (p.natDegree + (q.natDegree - p.natDegree) - p.natDegree)))).coeff
      (p.natDegree + (q.natDegree - p.natDegree)) =
    0

tactic: simp only [coeff_mul_X_pow, coeff_neg, coeff_C_mul, add_tsub_cancel_left, coeff_add]
state_before: case neg.a
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
h0 : (C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p)).natDegree = q.natDegree
⊢ (C p.leadingCoeff * q +
          -(C q.leadingCoeff * (p * X ^ (p.natDegree + (q.natDegree - p.natDegree) - p.natDegree)))).coeff
      (p.natDegree + (q.natDegree - p.natDegree)) =
    0
state_after: case neg.a
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
h0 : (C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p)).natDegree = q.natDegree
⊢ p.leadingCoeff * q.coeff (p.natDegree + (q.natDegree - p.natDegree)) + -(q.leadingCoeff * p.coeff p.natDegree) = 0

tactic: rw [add_comm p.natDegree, tsub_add_cancel_of_le h, ← leadingCoeff, ← leadingCoeff, comm,
  add_right_neg]
state_before: case neg.a
R : Type u_1
inst✝ : Ring R
p q : R[X]
comm : p.leadingCoeff * q.leadingCoeff = q.leadingCoeff * p.leadingCoeff
h : p.natDegree ≤ q.natDegree
hq : 0 < q.natDegree
hp : ¬p = 0
h0 : (C p.leadingCoeff * q + -(C q.leadingCoeff * X ^ (q.natDegree - p.natDegree) * p)).natDegree = q.natDegree
⊢ p.leadingCoeff * q.coeff (p.natDegree + (q.natDegree - p.natDegree)) + -(q.leadingCoeff * p.coeff p.natDegree) = 0
state_after: no goals