-- Mathlib/.lake/packages/lean4/src/lean/Std/Tactic/BVDecide/LRAT/Internal/Formula/Lemmas.lean
theorem deleteOne_preserves_strongAssignmentsInvariant {n : Nat} (f : DefaultFormula n) (id : Nat) :
    StrongAssignmentsInvariant f → StrongAssignmentsInvariant (deleteOne f id)

Proof state:
case inl.h.isTrue.intro.intro
n : Nat
f : DefaultFormula n
id : Nat
hsize : f.assignments.size = n
hsize' : (f.deleteOne id).assignments.size = n
i : PosFin n
b : Bool
i_in_bounds : i.val < f.assignments.size
c : DefaultClause n
heq : f.clauses[id]! = some c
l : Literal (PosFin n)
hl : c = { clause := [l], nodupkey := ⋯, nodup := ⋯ }
l_eq_i : l.fst.val = i.val
l_ne_b : l.snd = !b
hb✝ : hasAssignment b (removeAssignment (!b) f.assignments[i.val]) = true
hb : hasAssignment b f.assignments[i.val] = true
hf : some (unit (i, b)) ∈ f.clauses.toList
h✝ : id < f.clauses.size
idx : Nat
hbound : idx < f.clauses.toList.length
hidx : f.clauses.toList[idx] = some (unit (i, b))
idx_in_bounds : idx < (f.clauses.toList.set id none).length
⊢ ∃ n_1, (f.clauses.toList.set id none).get n_1 = f.clauses.toList[idx]

Tactic:
apply Exists.intro ⟨idx, idx_in_bounds⟩

Result:
case inl.h.isTrue.intro.intro
n : Nat
f : DefaultFormula n
id : Nat
hsize : f.assignments.size = n
hsize' : (f.deleteOne id).assignments.size = n
i : PosFin n
b : Bool
i_in_bounds : i.val < f.assignments.size
c : DefaultClause n
heq : f.clauses[id]! = some c
l : Literal (PosFin n)
hl : c = { clause := [l], nodupkey := ⋯, nodup := ⋯ }
l_eq_i : l.fst.val = i.val
l_ne_b : l.snd = !b
hb✝ : hasAssignment b (removeAssignment (!b) f.assignments[i.val]) = true
hb : hasAssignment b f.assignments[i.val] = true
hf : some (unit (i, b)) ∈ f.clauses.toList
h✝ : id < f.clauses.size
idx : Nat
hbound : idx < f.clauses.toList.length
hidx : f.clauses.toList[idx] = some (unit (i, b))
idx_in_bounds : idx < (f.clauses.toList.set id none).length
⊢ (f.clauses.toList.set id none).get ⟨idx, idx_in_bounds⟩ = f.clauses.toList[idx]

Proof state:
n : Nat
f : DefaultFormula n
id : Nat
hsize : f.assignments.size = n
hsize' : (f.deleteOne id).assignments.size = n
i : PosFin n
b : Bool
i_in_bounds : i.val < f.assignments.size
c : DefaultClause n
heq : f.clauses[id]! = some c
l : Literal (PosFin n)
hl : c = { clause := [l], nodupkey := ⋯, nodup := ⋯ }
l_eq_i : l.fst.val = i.val
l_ne_b : l.snd = !b
hb✝ : hasAssignment b (removeAssignment (!b) f.assignments[i.val]) = true
hb : hasAssignment b f.assignments[i.val] = true
hf : some (unit (i, b)) ∈ f.clauses.toList
h✝ : id < f.clauses.size
idx : Nat
hbound : idx < f.clauses.toList.length
hidx : f.clauses.toList[idx] = some (unit (i, b))
⊢ idx < (f.clauses.toList.set id none).length

Tactic:
simp only [List.length_set]

Result:
n : Nat
f : DefaultFormula n
id : Nat
hsize : f.assignments.size = n
hsize' : (f.deleteOne id).assignments.size = n
i : PosFin n
b : Bool
i_in_bounds : i.val < f.assignments.size
c : DefaultClause n
heq : f.clauses[id]! = some c
l : Literal (PosFin n)
hl : c = { clause := [l], nodupkey := ⋯, nodup := ⋯ }
l_eq_i : l.fst.val = i.val
l_ne_b : l.snd = !b
hb✝ : hasAssignment b (removeAssignment (!b) f.assignments[i.val]) = true
hb : hasAssignment b f.assignments[i.val] = true
hf : some (unit (i, b)) ∈ f.clauses.toList
h✝ : id < f.clauses.size
idx : Nat
hbound : idx < f.clauses.toList.length
hidx : f.clauses.toList[idx] = some (unit (i, b))
⊢ idx < f.clauses.toList.length

Proof state:
n : Nat
f : DefaultFormula n
id : Nat
hsize : f.assignments.size = n
hsize' : (f.deleteOne id).assignments.size = n
i : PosFin n
b : Bool
i_in_bounds : i.val < f.assignments.size
c : DefaultClause n
heq✝ : f.clauses[id]! = some c
l : Literal (PosFin n)
hl : c = { clause := [l], nodupkey := ⋯, nodup := ⋯ }
l_eq_i : l.fst.val = i.val
hb✝ : hasAssignment b (removeAssignment (!b) f.assignments[i.val]) = true
hb : hasAssignment b f.assignments[i.val] = true
hf : some (unit (i, b)) ∈ f.clauses.toList
h✝ : id < f.clauses.size
idx : Nat
hbound : idx < f.clauses.toList.length
hidx : f.clauses.toList[idx] = some (unit (i, b))
idx_in_bounds : idx < (f.clauses.toList.set id none).length
id_eq_idx : id = idx
idx_in_bounds2 : idx < f.clauses.size
heq : (i, b) = l
l_ne_b : b = !b
⊢ False

Tactic:
simp at l_ne_b

Result:
no goals

Proof state:
n : Nat
f : DefaultFormula n
id : Nat
hsize : f.assignments.size = n
hf : ∀ (i : PosFin n) (b : Bool), hasAssignment b f.assignments[i.val] = true → unit (i, b) ∈ f.toList
hsize' : (f.deleteOne id).assignments.size = n
i : PosFin n
b : Bool
hb : hasAssignment b (f.deleteOne id).assignments[i.val] = true
i_in_bounds : i.val < f.assignments.size
c : DefaultClause n
heq✝ : f.clauses[id]! = some c
x✝ : Option (DefaultClause n)
l : Literal (PosFin n)
nodupkey✝ : ∀ (l_1 : PosFin n), ¬(l_1, true) ∈ [l] ∨ ¬(l_1, false) ∈ [l]
nodup✝ : [l].Nodup
heq : c = { clause := [l], nodupkey := nodupkey✝, nodup := nodup✝ }
hl : ¬l = (l.fst, false) ∧ ¬l = (l.fst, true)
⊢ unit (i, b) ∈
    { clauses := f.clauses.set! id none, rupUnits := f.rupUnits, ratUnits := f.ratUnits,
        assignments := f.assignments.modify l.fst.val (removeAssignment l.snd) }.toList

Tactic:
by_cases hl2 : l.2

Result:
case pos
n : Nat
f : DefaultFormula n
id : Nat
hsize : f.assignments.size = n
hf : ∀ (i : PosFin n) (b : Bool), hasAssignment b f.assignments[i.val] = true → unit (i, b) ∈ f.toList
hsize' : (f.deleteOne id).assignments.size = n
i : PosFin n
b : Bool
hb : hasAssignment b (f.deleteOne id).assignments[i.val] = true
i_in_bounds : i.val < f.assignments.size
c : DefaultClause n
heq✝ : f.clauses[id]! = some c
x✝ : Option (DefaultClause n)
l : Literal (PosFin n)
nodupkey✝ : ∀ (l_1 : PosFin n), ¬(l_1, true) ∈ [l] ∨ ¬(l_1, false) ∈ [l]
nodup✝ : [l].Nodup
heq : c = { clause := [l], nodupkey := nodupkey✝, nodup := nodup✝ }
hl : ¬l = (l.fst, false) ∧ ¬l = (l.fst, true)
hl2 : l.snd = true
⊢ unit (i, b) ∈
    { clauses := f.clauses.set! id none, rupUnits := f.rupUnits, ratUnits := f.ratUnits,
        assignments := f.assignments.modify l.fst.val (removeAssignment l.snd) }.toList

case neg
n : Nat
f : DefaultFormula n
id : Nat
hsize : f.assignments.size = n
hf : ∀ (i : PosFin n) (b : Bool), hasAssignment b f.assignments[i.val] = true → unit (i, b) ∈ f.toList
hsize' : (f.deleteOne id).assignments.size = n
i : PosFin n
b : Bool
hb : hasAssignment b (f.deleteOne id).assignments[i.val] = true
i_in_bounds : i.val < f.assignments.size
c : DefaultClause n
heq✝ : f.clauses[id]! = some c
x✝ : Option (DefaultClause n)
l : Literal (PosFin n)
nodupkey✝ : ∀ (l_1 : PosFin n), ¬(l_1, true) ∈ [l] ∨ ¬(l_1, false) ∈ [l]
nodup✝ : [l].Nodup
heq : c = { clause := [l], nodupkey := nodupkey✝, nodup := nodup✝ }
hl : ¬l = (l.fst, false) ∧ ¬l = (l.fst, true)
hl2 : ¬l.snd = true
⊢ unit (i, b) ∈
    { clauses := f.clauses.set! id none, rupUnits := f.rupUnits, ratUnits := f.ratUnits,
        assignments := f.assignments.modify l.fst.val (removeAssignment l.snd) }.toList

Proof state:
n : Nat
f : DefaultFormula n
id : Nat
hsize : f.assignments.size = n
hsize' : (f.deleteOne id).assignments.size = n
i : PosFin n
b : Bool
i_in_bounds : i.val < f.assignments.size
c : DefaultClause n
heq : f.clauses[id]! = some c
l : Literal (PosFin n)
hl : c = { clause := [l], nodupkey := ⋯, nodup := ⋯ }
l_eq_i : l.fst.val = i.val
l_ne_b : l.snd = !b
hb✝ : hasAssignment b (removeAssignment (!b) f.assignments[i.val]) = true
hb : hasAssignment b f.assignments[i.val] = true
hf : some (unit (i, b)) ∈ f.clauses.toList
h✝ : id < f.clauses.size
idx : Nat
hbound : idx < f.clauses.toList.length
hidx : f.clauses.toList[idx] = some (unit (i, b))
idx_in_bounds : idx < (f.clauses.toList.set id none).length
id_eq_idx : id = idx
⊢ idx < f.1.toList.length

Tactic:
exact hbound

Result:
no goals