[ODFF] SERIESSUM needs a rule for x=0

Hi members,

in SERIESSUM the argument x=0 is allowed. But it will erase an error for 
negative exponents.

Currently OOo3.0 and Excel return an #VALUE! error in all cases. But I 
think, that should not be the definition in the spec. SERIESSUM is a 
tool to evaluate polynomials. Therefore 0^0 should be set to 1, at least 
if N and M are non-negative integers.

My proposal is to define a constraint, that the argument x=0 results in 
an error, if any of the exponents, which are generated from N and M, are 
negative.
If all of the exponents are non-negative, then 0^0 should be set to 1 
and 0^(exponent>0) should be set to 0.
I see no use case in a spreadsheet, where this will give problems. Do 
you see any obstacle?

My proposal seems to be the way Gnumeric implements SERIESSUM.

kind regards
Regina