simp only [insert] at h
case mp.h.inl.h
n : Nat
f : DefaultFormula n
c1 c2 : DefaultClause n
c2_ne_c1 : ¬c2 = c1
h : some c2 ∈ (f.insert c1).clauses.data
⊢ some c2 ∈ f.clauses.data
case mp.h.inl.h
n : Nat
f : DefaultFormula n
c1 c2 : DefaultClause n
c2_ne_c1 : ¬c2 = c1
h :
  some c2 ∈
    (match c1.isUnit with
        | none =>
          { clauses := f.clauses.push (some c1), rupUnits := f.rupUnits, ratUnits := f.ratUnits,
            assignments := f.assignments }
        | some (l, true) =>
          { clauses := f.clauses.push (some c1), rupUnits := f.rupUnits, ratUnits := f.ratUnits,
            assignments := f.assignments.modify l.val addPosAssignment }
        | some (l, false) =>
          { clauses := f.clauses.push (some c1), rupUnits := f.rupUnits, ratUnits := f.ratUnits,
            assignments := f.assignments.modify l.val addNegAssignment }).clauses.data
⊢ some c2 ∈ f.clauses.data