-- Mathlib/Topology/Homotopy/HSpaces.lean
theorem delayReflRight_zero (γ : Path x y) : delayReflRight 0 γ = γ.trans (Path.refl y)

Proof state:
case pos
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ↑t ≤ 1 / 2
⊢ γ (qRight (t, 0)) = γ ⟨2 * ↑t, ⋯⟩

Tactic:
apply congr_arg γ

Result:
case pos
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ↑t ≤ 1 / 2
⊢ qRight (t, 0) = ⟨2 * ↑t, ⋯⟩

Proof state:
case pos
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ↑t ≤ 1 / 2
⊢ qRight (t, 0) = ⟨2 * ↑t, ⋯⟩

Tactic:
ext1

Result:
case pos.a
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ↑t ≤ 1 / 2
⊢ ↑(qRight (t, 0)) = ↑⟨2 * ↑t, ⋯⟩

Proof state:
case pos
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ↑t ≤ 1 / 2
⊢ γ (qRight (t, 0)) = γ ⟨2 * ↑t, ⋯⟩

case neg
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ¬↑t ≤ 1 / 2
⊢ γ (qRight (t, 0)) = y

Tactic:
swap

Result:
case neg
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ¬↑t ≤ 1 / 2
⊢ γ (qRight (t, 0)) = y

case pos
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ↑t ≤ 1 / 2
⊢ γ (qRight (t, 0)) = γ ⟨2 * ↑t, ⋯⟩

Proof state:
case neg
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ¬↑t ≤ 1 / 2
⊢ γ (qRight (t, 0)) = y

case pos
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ↑t ≤ 1 / 2
⊢ γ (qRight (t, 0)) = γ ⟨2 * ↑t, ⋯⟩

Tactic:
on_goal 1 => conv_rhs => rw [← γ.target]

Result:
case neg
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ¬↑t ≤ 1 / 2
⊢ γ (qRight (t, 0)) = γ 1

case pos
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ↑t ≤ 1 / 2
⊢ γ (qRight (t, 0)) = γ ⟨2 * ↑t, ⋯⟩

Proof state:
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
⊢ delayReflRight 0 γ = γ.trans (refl y)

Tactic:
ext t

Result:
case a.h
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
⊢ (delayReflRight 0 γ) t = (γ.trans (refl y)) t

Proof state:
case a.h
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
⊢ γ (qRight (t, 0)) = if h : ↑t ≤ 1 / 2 then γ ⟨2 * ↑t, ⋯⟩ else y

Tactic:
split_ifs with h

Result:
case pos
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ↑t ≤ 1 / 2
⊢ γ (qRight (t, 0)) = γ ⟨2 * ↑t, ⋯⟩

case neg
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ¬↑t ≤ 1 / 2
⊢ γ (qRight (t, 0)) = y

Proof state:
case a.h
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
⊢ (delayReflRight 0 γ) t = (γ.trans (refl y)) t

Tactic:
simp only [delayReflRight, trans_apply, refl_extend, Path.coe_mk_mk, Function.comp_apply,
  refl_apply]

Result:
case a.h
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
⊢ γ (qRight (t, 0)) = if h : ↑t ≤ 1 / 2 then γ ⟨2 * ↑t, ⋯⟩ else y

Proof state:
case pos.a
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ↑t ≤ 1 / 2
⊢ ↑(qRight (t, 0)) = ↑⟨2 * ↑t, ⋯⟩

Tactic:
rw [qRight_zero_right]

Result:
case pos.a
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ↑t ≤ 1 / 2
⊢ (if ↑t ≤ 1 / 2 then 2 * ↑t else 1) = ↑⟨2 * ↑t, ⋯⟩

Proof state:
case neg
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ¬↑t ≤ 1 / 2
⊢ γ (qRight (t, 0)) = γ 1

case pos
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ↑t ≤ 1 / 2
⊢ γ (qRight (t, 0)) = γ ⟨2 * ↑t, ⋯⟩

Tactic:
all_goals apply congr_arg γ; ext1; rw [qRight_zero_right]

Result:
case neg.a
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ¬↑t ≤ 1 / 2
⊢ (if ↑t ≤ 1 / 2 then 2 * ↑t else 1) = ↑1

case pos.a
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ↑t ≤ 1 / 2
⊢ (if ↑t ≤ 1 / 2 then 2 * ↑t else 1) = ↑⟨2 * ↑t, ⋯⟩

Proof state:
case neg
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ¬↑t ≤ 1 / 2
⊢ γ (qRight (t, 0)) = y

Tactic:
conv_rhs => rw [← γ.target]

Result:
case neg
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ¬↑t ≤ 1 / 2
⊢ γ (qRight (t, 0)) = γ 1

Proof state:
case neg.a
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ¬↑t ≤ 1 / 2
⊢ (if ↑t ≤ 1 / 2 then 2 * ↑t else 1) = ↑1

case pos.a
X : Type u
inst✝ : TopologicalSpace X
x y : X
γ : Path x y
t : ↑I
h : ↑t ≤ 1 / 2
⊢ (if ↑t ≤ 1 / 2 then 2 * ↑t else 1) = ↑⟨2 * ↑t, ⋯⟩

Tactic:
exacts [if_neg h, if_pos h]

Result:
no goals