ex series(const relational & s, int order) const;
ex subs(const lst & ls, const lst & lr) const;
ex normal(lst &sym_lst, lst &repl_lst, int level=0) const;
ex series(const relational & s, int order) const;
ex subs(const lst & ls, const lst & lr) const;
ex normal(lst &sym_lst, lst &repl_lst, int level=0) const;