-- Mathlib/NumberTheory/Padics/PadicNorm.lean
theorem nonarchimedean_aux {q r : ℚ} (h : padicValRat p q ≤ padicValRat p r) :
    padicNorm p (q + r) ≤ max (padicNorm p q) (padicNorm p r) :=
  have hnqp : padicNorm p q ≥ 0 := padicNorm.nonneg _
  have hnrp : padicNorm p r ≥ 0 := padicNorm.nonneg _
  if hq : q = 0 then by simp [hq, max_eq_right hnrp, le_max_right]
  else
    if hr : r = 0 then by simp [hr, max_eq_left hnqp, le_max_left]
    else
      if hqr : q + r = 0 then le_trans (by simpa [hqr] using hnqp) (le_max_left _ _)
      else by
        unfold padicNorm; split_ifs
        apply le_max_iff.2
        left
        apply zpow_le_zpow_right₀
        · exact mod_cast le_of_lt hp.1.one_lt
        · apply neg_le_neg
          have : padicValRat p q = min (padicValRat p q) (padicValRat p r) := (min_eq_left h).symm
          rw [this]
          exact min_le_padicValRat_add hqr

Proof state:
case h
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
⊢ ↑p ^ (-padicValRat p (q + r)) ≤ ↑p ^ (-padicValRat p q)

Tactic:
apply zpow_le_zpow_right₀

Result:
case h.ha
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
⊢ 1 ≤ ↑p

case h.hmn
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
⊢ -padicValRat p (q + r) ≤ -padicValRat p q

Proof state:
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : r = 0
⊢ padicNorm p (q + r) ≤ padicNorm p q ⊔ padicNorm p r

Tactic:
simp [hr, max_eq_left hnqp, le_max_left]

Result:
no goals

Proof state:
case h.hmn.a
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
⊢ padicValRat p q ≤ padicValRat p (q + r)

Tactic:
have : padicValRat p q = min (padicValRat p q) (padicValRat p r) := (min_eq_left h).symm

Result:
case h.hmn.a
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
this : padicValRat p q = padicValRat p q ⊓ padicValRat p r
⊢ padicValRat p q ≤ padicValRat p (q + r)

Proof state:
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
⊢ (if q + r = 0 then 0 else ↑p ^ (-padicValRat p (q + r))) ≤
    (if q = 0 then 0 else ↑p ^ (-padicValRat p q)) ⊔ if r = 0 then 0 else ↑p ^ (-padicValRat p r)

Tactic:
split_ifs

Result:
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
⊢ ↑p ^ (-padicValRat p (q + r)) ≤ ↑p ^ (-padicValRat p q) ⊔ ↑p ^ (-padicValRat p r)

Proof state:
case h.hmn.a
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
this : padicValRat p q = padicValRat p q ⊓ padicValRat p r
⊢ padicValRat p q ⊓ padicValRat p r ≤ padicValRat p (q + r)

Tactic:
exact min_le_padicValRat_add hqr

Result:
no goals

Proof state:
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
⊢ ↑p ^ (-padicValRat p (q + r)) ≤ ↑p ^ (-padicValRat p q) ⊔ ↑p ^ (-padicValRat p r)

Tactic:
apply le_max_iff.2

Result:
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
⊢ ↑p ^ (-padicValRat p (q + r)) ≤ ↑p ^ (-padicValRat p q) ∨ ↑p ^ (-padicValRat p (q + r)) ≤ ↑p ^ (-padicValRat p r)

Proof state:
case h.hmn.a
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
this : padicValRat p q = padicValRat p q ⊓ padicValRat p r
⊢ padicValRat p q ≤ padicValRat p (q + r)

Tactic:
rw [this]

Result:
case h.hmn.a
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
this : padicValRat p q = padicValRat p q ⊓ padicValRat p r
⊢ padicValRat p q ⊓ padicValRat p r ≤ padicValRat p (q + r)

Proof state:
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : q = 0
⊢ padicNorm p (q + r) ≤ padicNorm p q ⊔ padicNorm p r

Tactic:
simp [hq, max_eq_right hnrp, le_max_right]

Result:
no goals

Proof state:
case h.ha
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
⊢ 1 ≤ ↑p

Tactic:
exact mod_cast le_of_lt hp.1.one_lt

Result:
no goals

Proof state:
case h.hmn
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
⊢ -padicValRat p (q + r) ≤ -padicValRat p q

Tactic:
apply neg_le_neg

Result:
case h.hmn.a
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
⊢ padicValRat p q ≤ padicValRat p (q + r)

Proof state:
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : q + r = 0
⊢ padicNorm p (q + r) ≤ padicNorm p q

Tactic:
simpa [hqr] using hnqp

Result:
no goals

Proof state:
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
⊢ padicNorm p (q + r) ≤ padicNorm p q ⊔ padicNorm p r

Tactic:
unfold padicNorm

Result:
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
⊢ (if q + r = 0 then 0 else ↑p ^ (-padicValRat p (q + r))) ≤
    (if q = 0 then 0 else ↑p ^ (-padicValRat p q)) ⊔ if r = 0 then 0 else ↑p ^ (-padicValRat p r)

Proof state:
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
⊢ ↑p ^ (-padicValRat p (q + r)) ≤ ↑p ^ (-padicValRat p q) ∨ ↑p ^ (-padicValRat p (q + r)) ≤ ↑p ^ (-padicValRat p r)

Tactic:
left

Result:
case h
p : ℕ
hp : Fact (Nat.Prime p)
q r : ℚ
h : padicValRat p q ≤ padicValRat p r
hnqp : padicNorm p q ≥ 0
hnrp : padicNorm p r ≥ 0
hq : ¬q = 0
hr : ¬r = 0
hqr : ¬q + r = 0
⊢ ↑p ^ (-padicValRat p (q + r)) ≤ ↑p ^ (-padicValRat p q)