Hi again, pseries::power_const() has second argument int deg that allows negative values of deg. If one calls this method with negative deg then the line co.reserve(deg); will cause MemoryError as (unsigned)deg gets really big. My questions are: 1) Is there any sense using negative deg? If yes, then the above indicates a bug. If no, then an exception should be thrown. 2) In case negative deg is valid, then is there a reason why power_const() method needs this argument (and methods mul_const(),etc don't)? In the interface to python, I have used the following rule to find the default value for deg: If p==pseries(...) and n is integer, then deg in p.power_const(n,deg) is found as follows ldeg = abs(n * p.ldegree(p.get_var())) deg = abs(n * p.degree(p.get_var())) deg = max(ldeg,deg) + 2 With this rule, I have found that equation (p^n)^m == p^(n*m) for all integers m,n (also negative). holds (and therefore seems sensible to me). Do you see any faults in this rule? Thanks, Pearu