-- Mathlib/MeasureTheory/Integral/SetToL1.lean
theorem setToL1_add_left' (hT : DominatedFinMeasAdditive μ T C)
    (hT' : DominatedFinMeasAdditive μ T' C') (hT'' : DominatedFinMeasAdditive μ T'' C'')
    (h_add : ∀ s, MeasurableSet s → μ s < ∞ → T'' s = T s + T' s) (f : α →₁[μ] E) :
    setToL1 hT'' f = setToL1 hT f + setToL1 hT' f

Proof state:
case h
α : Type u_1
E : Type u_2
F : Type u_3
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℝ F
m : MeasurableSpace α
μ : Measure α
inst✝ : CompleteSpace F
T T' T'' : Set α → E →L[ℝ] F
C C' C'' : ℝ
hT : DominatedFinMeasAdditive μ T C
hT' : DominatedFinMeasAdditive μ T' C'
hT'' : DominatedFinMeasAdditive μ T'' C''
h_add : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → T'' s = T s + T' s
f✝ : ↥(Lp E 1 μ)
f : ↥(simpleFunc E 1 μ)
⊢ ((setToL1 hT + setToL1 hT').comp (coeToLp α E ℝ)) f = (setToL1SCLM α E μ hT'') f

Tactic:
suffices setToL1 hT f + setToL1 hT' f = setToL1SCLM α E μ hT'' f by rw [← this]; congr

Result:
case h
α : Type u_1
E : Type u_2
F : Type u_3
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℝ F
m : MeasurableSpace α
μ : Measure α
inst✝ : CompleteSpace F
T T' T'' : Set α → E →L[ℝ] F
C C' C'' : ℝ
hT : DominatedFinMeasAdditive μ T C
hT' : DominatedFinMeasAdditive μ T' C'
hT'' : DominatedFinMeasAdditive μ T'' C''
h_add : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → T'' s = T s + T' s
f✝ : ↥(Lp E 1 μ)
f : ↥(simpleFunc E 1 μ)
⊢ (setToL1 hT) ↑f + (setToL1 hT') ↑f = (setToL1SCLM α E μ hT'') f

Proof state:
α : Type u_1
E : Type u_2
F : Type u_3
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℝ F
m : MeasurableSpace α
μ : Measure α
inst✝ : CompleteSpace F
T T' T'' : Set α → E →L[ℝ] F
C C' C'' : ℝ
hT : DominatedFinMeasAdditive μ T C
hT' : DominatedFinMeasAdditive μ T' C'
hT'' : DominatedFinMeasAdditive μ T'' C''
h_add : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → T'' s = T s + T' s
f : ↥(Lp E 1 μ)
this : setToL1 hT'' = setToL1 hT + setToL1 hT'
⊢ (setToL1 hT'') f = (setToL1 hT) f + (setToL1 hT') f

Tactic:
rw [this, ContinuousLinearMap.add_apply]

Result:
no goals

Proof state:
case h
α : Type u_1
E : Type u_2
F : Type u_3
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℝ F
m : MeasurableSpace α
μ : Measure α
inst✝ : CompleteSpace F
T T' T'' : Set α → E →L[ℝ] F
C C' C'' : ℝ
hT : DominatedFinMeasAdditive μ T C
hT' : DominatedFinMeasAdditive μ T' C'
hT'' : DominatedFinMeasAdditive μ T'' C''
h_add : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → T'' s = T s + T' s
f✝ : ↥(Lp E 1 μ)
f : ↥(simpleFunc E 1 μ)
⊢ (setToL1 hT) ↑f + (setToL1 hT') ↑f = (setToL1SCLM α E μ hT'') f

Tactic:
rw [setToL1_eq_setToL1SCLM, setToL1_eq_setToL1SCLM,
  setToL1SCLM_add_left' hT hT' hT'' h_add]

Result:
no goals

Proof state:
α : Type u_1
E : Type u_2
F : Type u_3
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℝ F
m : MeasurableSpace α
μ : Measure α
inst✝ : CompleteSpace F
T T' T'' : Set α → E →L[ℝ] F
C C' C'' : ℝ
hT : DominatedFinMeasAdditive μ T C
hT' : DominatedFinMeasAdditive μ T' C'
hT'' : DominatedFinMeasAdditive μ T'' C''
h_add : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → T'' s = T s + T' s
f : ↥(Lp E 1 μ)
⊢ setToL1 hT'' = setToL1 hT + setToL1 hT'

Tactic:
refine ContinuousLinearMap.extend_unique (setToL1SCLM α E μ hT'') _ _ _ _ ?_

Result:
α : Type u_1
E : Type u_2
F : Type u_3
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℝ F
m : MeasurableSpace α
μ : Measure α
inst✝ : CompleteSpace F
T T' T'' : Set α → E →L[ℝ] F
C C' C'' : ℝ
hT : DominatedFinMeasAdditive μ T C
hT' : DominatedFinMeasAdditive μ T' C'
hT'' : DominatedFinMeasAdditive μ T'' C''
h_add : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → T'' s = T s + T' s
f : ↥(Lp E 1 μ)
⊢ (setToL1 hT + setToL1 hT').comp (coeToLp α E ℝ) = setToL1SCLM α E μ hT''

Proof state:
α : Type u_1
E : Type u_2
F : Type u_3
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℝ F
m : MeasurableSpace α
μ : Measure α
inst✝ : CompleteSpace F
T T' T'' : Set α → E →L[ℝ] F
C C' C'' : ℝ
hT : DominatedFinMeasAdditive μ T C
hT' : DominatedFinMeasAdditive μ T' C'
hT'' : DominatedFinMeasAdditive μ T'' C''
h_add : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → T'' s = T s + T' s
f✝ : ↥(Lp E 1 μ)
f : ↥(simpleFunc E 1 μ)
this : (setToL1 hT) ↑f + (setToL1 hT') ↑f = (setToL1SCLM α E μ hT'') f
⊢ ((setToL1 hT + setToL1 hT').comp (coeToLp α E ℝ)) f = (setToL1SCLM α E μ hT'') f

Tactic:
rw [← this]

Result:
α : Type u_1
E : Type u_2
F : Type u_3
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℝ F
m : MeasurableSpace α
μ : Measure α
inst✝ : CompleteSpace F
T T' T'' : Set α → E →L[ℝ] F
C C' C'' : ℝ
hT : DominatedFinMeasAdditive μ T C
hT' : DominatedFinMeasAdditive μ T' C'
hT'' : DominatedFinMeasAdditive μ T'' C''
h_add : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → T'' s = T s + T' s
f✝ : ↥(Lp E 1 μ)
f : ↥(simpleFunc E 1 μ)
this : (setToL1 hT) ↑f + (setToL1 hT') ↑f = (setToL1SCLM α E μ hT'') f
⊢ ((setToL1 hT + setToL1 hT').comp (coeToLp α E ℝ)) f = (setToL1 hT) ↑f + (setToL1 hT') ↑f

Proof state:
α : Type u_1
E : Type u_2
F : Type u_3
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℝ F
m : MeasurableSpace α
μ : Measure α
inst✝ : CompleteSpace F
T T' T'' : Set α → E →L[ℝ] F
C C' C'' : ℝ
hT : DominatedFinMeasAdditive μ T C
hT' : DominatedFinMeasAdditive μ T' C'
hT'' : DominatedFinMeasAdditive μ T'' C''
h_add : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → T'' s = T s + T' s
f : ↥(Lp E 1 μ)
⊢ (setToL1 hT + setToL1 hT').comp (coeToLp α E ℝ) = setToL1SCLM α E μ hT''

Tactic:
ext1 f

Result:
case h
α : Type u_1
E : Type u_2
F : Type u_3
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℝ F
m : MeasurableSpace α
μ : Measure α
inst✝ : CompleteSpace F
T T' T'' : Set α → E →L[ℝ] F
C C' C'' : ℝ
hT : DominatedFinMeasAdditive μ T C
hT' : DominatedFinMeasAdditive μ T' C'
hT'' : DominatedFinMeasAdditive μ T'' C''
h_add : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → T'' s = T s + T' s
f✝ : ↥(Lp E 1 μ)
f : ↥(simpleFunc E 1 μ)
⊢ ((setToL1 hT + setToL1 hT').comp (coeToLp α E ℝ)) f = (setToL1SCLM α E μ hT'') f

Proof state:
α : Type u_1
E : Type u_2
F : Type u_3
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℝ F
m : MeasurableSpace α
μ : Measure α
inst✝ : CompleteSpace F
T T' T'' : Set α → E →L[ℝ] F
C C' C'' : ℝ
hT : DominatedFinMeasAdditive μ T C
hT' : DominatedFinMeasAdditive μ T' C'
hT'' : DominatedFinMeasAdditive μ T'' C''
h_add : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → T'' s = T s + T' s
f : ↥(Lp E 1 μ)
⊢ (setToL1 hT'') f = (setToL1 hT) f + (setToL1 hT') f

Tactic:
suffices setToL1 hT'' = setToL1 hT + setToL1 hT' by rw [this, ContinuousLinearMap.add_apply]

Result:
α : Type u_1
E : Type u_2
F : Type u_3
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
inst✝² : NormedAddCommGroup F
inst✝¹ : NormedSpace ℝ F
m : MeasurableSpace α
μ : Measure α
inst✝ : CompleteSpace F
T T' T'' : Set α → E →L[ℝ] F
C C' C'' : ℝ
hT : DominatedFinMeasAdditive μ T C
hT' : DominatedFinMeasAdditive μ T' C'
hT'' : DominatedFinMeasAdditive μ T'' C''
h_add : ∀ (s : Set α), MeasurableSet s → μ s < ⊤ → T'' s = T s + T' s
f : ↥(Lp E 1 μ)
⊢ setToL1 hT'' = setToL1 hT + setToL1 hT'