split <;> simp only
n : Nat
f : DefaultFormula n
id : Nat
⊢ (match f.clauses[id]! with
      | none => { clauses := f.clauses, rupUnits := f.rupUnits, ratUnits := f.ratUnits, assignments := f.assignments }
      | some { clause := [l], nodupkey := nodupkey, nodup := nodup } =>
        { clauses := f.clauses.set! id none, rupUnits := f.rupUnits, ratUnits := f.ratUnits,
          assignments := f.assignments.modify l.fst.val (removeAssignment l.snd) }
      | some val =>
        { clauses := f.clauses.set! id none, rupUnits := f.rupUnits, ratUnits := f.ratUnits,
          assignments := f.assignments }).rupUnits =
    f.rupUnits
no goals