* Improved the speed of subs(), normal(), to_rational() and to_polynomial()
by the use of maps instead of lists. The old forms
subs(const lst & ls, const lst & lr, unsigned options)
* Improved the speed of subs(), normal(), to_rational() and to_polynomial()
by the use of maps instead of lists. The old forms
subs(const lst & ls, const lst & lr, unsigned options)