[Maxima-bugs] [maxima:bugs] #4597 residue should check if taylor series is a power series

[Barton W. <wil...@us...>]

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**[bugs:#4597] residue should check if taylor series is a power series**

**Status:** open
**Group:** None
**Created:** Sat Aug 16, 2025 10:09 PM UTC by Barton Willis
**Last Updated:** Sat Aug 16, 2025 10:09 PM UTC
**Owner:** nobody


Wrong--the residue of   `x -> log(1-x)/(1-x)` at 1 does not exist, but Maxima says it does:
~~~
(%i3)	residue(log(1-x)/(1-x),x,1);
(%o3)	-log(x-1)-log(-1)

(%i4)	build_info();
(%o4)	build_info(version="5.48.1",...)
~~~

The function `residue` assumes that `taylor` returns a power series, but for this expression it does not:
~~~
(%i6)	residue(log(1-x)/(1-x),x,1);
1" Call   "taylor[-(log(1-x)/(x-1)),x,1,1]

1" Return "taylor(-log(-1)-log(x-1)+...)/(x-1)+...

(%o6)	-log(x-1)-log(-1)
~~~



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