let initialize (syst:system) sel var ari =
  sys := syst;
  selbairav := sel;
  variables := var;
  arities := ari;
  definedSymbols :=
        List.fold_left
          (fun set (t1,_) ->
                match t1 with
                  | Var _ -> set
                  | Term (str,_) -> SymbSet.add str set
          )
          SymbSet.empty
          sys