Module: Mathlib.Data.List.SplitBy

Goal state before:
pp: case h_1
α : Type u_1
r : α → α → Bool
b : α
l : List α
IH :
  ∀ {a : α} {g : List α} {gs : List (List α)},
    ¬[] ∈ gs →
      IsChain (fun b a ↦ ∃ ha hb, r (a.getLast ha) (b.head hb) = false) gs →
        (∀ (m : List α), m ∈ gs.head? → ∃ ha hb, r (m.getLast ha) ((g.reverse ++ [a]).head hb) = false) →
          IsChain (fun a b ↦ ∃ ha hb, r (a.getLast ha) (b.head hb) = false) (splitBy.loop r l a g gs)
a : α
g : List α
gs : List (List α)
hgs' : ¬[] ∈ gs
hgs : IsChain (fun b a ↦ ∃ ha hb, r (a.getLast ha) (b.head hb) = false) gs
hga : ∀ (m : List α), m ∈ gs.head? → ∃ ha hb, r (m.getLast ha) ((g.reverse ++ [a]).head hb) = false
x✝ : Bool
heq✝ : r a b = true
m : List α
hm : m ∈ gs.head?
ha : m ≠ []
w✝ : g.reverse ++ [a] ≠ []
H : r (m.getLast ha) ((g.reverse ++ [a]).head w✝) = false
⊢ r (m.getLast ha) ((g.reverse ++ [a]).head ?h_1✝) = false

pp: case h_1
α : Type u_1
r : α → α → Bool
b : α
l : List α
IH :
  ∀ {a : α} {g : List α} {gs : List (List α)},
    ¬[] ∈ gs →
      IsChain (fun b a ↦ ∃ ha hb, r (a.getLast ha) (b.head hb) = false) gs →
        (∀ (m : List α), m ∈ gs.head? → ∃ ha hb, r (m.getLast ha) ((g.reverse ++ [a]).head hb) = false) →
          IsChain (fun a b ↦ ∃ ha hb, r (a.getLast ha) (b.head hb) = false) (splitBy.loop r l a g gs)
a : α
g : List α
gs : List (List α)
hgs' : ¬[] ∈ gs
hgs : IsChain (fun b a ↦ ∃ ha hb, r (a.getLast ha) (b.head hb) = false) gs
hga : ∀ (m : List α), m ∈ gs.head? → ∃ ha hb, r (m.getLast ha) ((g.reverse ++ [a]).head hb) = false
x✝ : Bool
heq✝ : r a b = true
m : List α
hm : m ∈ gs.head?
ha : m ≠ []
w✝ : g.reverse ++ [a] ≠ []
H : r (m.getLast ha) ((g.reverse ++ [a]).head w✝) = false
⊢ g.reverse ++ [a] ≠ []

Tactic:
]

Goal state after:
case h_1
α : Type u_1
r : α → α → Bool
b : α
l : List α
IH :
  ∀ {a : α} {g : List α} {gs : List (List α)},
    ¬[] ∈ gs →
      IsChain (fun b a ↦ ∃ ha hb, r (a.getLast ha) (b.head hb) = false) gs →
        (∀ (m : List α), m ∈ gs.head? → ∃ ha hb, r (m.getLast ha) ((g.reverse ++ [a]).head hb) = false) →
          IsChain (fun a b ↦ ∃ ha hb, r (a.getLast ha) (b.head hb) = false) (splitBy.loop r l a g gs)
a : α
g : List α
gs : List (List α)
hgs' : ¬[] ∈ gs
hgs : IsChain (fun b a ↦ ∃ ha hb, r (a.getLast ha) (b.head hb) = false) gs
hga : ∀ (m : List α), m ∈ gs.head? → ∃ ha hb, r (m.getLast ha) ((g.reverse ++ [a]).head hb) = false
x✝ : Bool
heq✝ : r a b = true
m : List α
hm : m ∈ gs.head?
ha : m ≠ []
w✝ : g.reverse ++ [a] ≠ []
H : r (m.getLast ha) ((g.reverse ++ [a]).head w✝) = false
⊢ r (m.getLast ha) ((g.reverse ++ [a]).head ?h_1✝) = false

case h_1
α : Type u_1
r : α → α → Bool
b : α
l : List α
IH :
  ∀ {a : α} {g : List α} {gs : List (List α)},
    ¬[] ∈ gs →
      IsChain (fun b a ↦ ∃ ha hb, r (a.getLast ha) (b.head hb) = false) gs →
        (∀ (m : List α), m ∈ gs.head? → ∃ ha hb, r (m.getLast ha) ((g.reverse ++ [a]).head hb) = false) →
          IsChain (fun a b ↦ ∃ ha hb, r (a.getLast ha) (b.head hb) = false) (splitBy.loop r l a g gs)
a : α
g : List α
gs : List (List α)
hgs' : ¬[] ∈ gs
hgs : IsChain (fun b a ↦ ∃ ha hb, r (a.getLast ha) (b.head hb) = false) gs
hga : ∀ (m : List α), m ∈ gs.head? → ∃ ha hb, r (m.getLast ha) ((g.reverse ++ [a]).head hb) = false
x✝ : Bool
heq✝ : r a b = true
m : List α
hm : m ∈ gs.head?
ha : m ≠ []
w✝ : g.reverse ++ [a] ≠ []
H : r (m.getLast ha) ((g.reverse ++ [a]).head w✝) = false
⊢ g.reverse ++ [a] ≠ []