@code{(x^(-3)*y^(-2)*z).subs(1/(x*y)==c, subs_options::algebraic)} will
return @code{x^(-1)*c^2*z}.
-@strong{Note:} this only works for multiplications
+@strong{Please notice:} this only works for multiplications
and not for locating @code{x+y} within @code{x+y+z}.