Dear Vladimir V. Kisil,

Thanks very much for suggestion to use expand() method on e3 first.

And I have given a look at the source code at power::to_polynomial

 2688  ex power::to_polynomial(exmap & repl) const

 2689 {

 2690     if (exponent.info(info_flags::posint))

 2691         return pow(basis.to_rational(repl), exponent);

 2692     else if (exponent.info(info_flags::negint))

 2693     {

 2694         ex basis_pref = collect_common_factors(basis);

 2695         if (is_exactly_a<mul>(basis_pref) || is_exactly_a<power>(basis_pref)) {

 2696             // (A*B)^n will be automagically transformed to A^n*B^n

 2697             ex t = pow(basis_pref, exponent);

 2698             return t.to_polynomial(repl);

 2699         }

 2700         else

 2701             return pow(replace_with_symbol(pow(basis, _ex_1), repl), -exponent);

 2702     }

 2703     else

 2704         return replace_with_symbol(*this, repl);

 2705 }

and I wonfer if there is a typo on line 2691, the basis.to_rational can be replaced with basis.to_polynomial?

Best regards!