The gen() method for power series over power series works incorrectly

[haraldschilly]

If I type the following:

S1 = LazyPowerSeriesRing(ZZ)
S2 = LazyPowerSeriesRing(S1)
y = S2.gen()
y.coefficient(1) == 1

I get True, and

y.coefficient(1).coefficient(0)

gets me the "'int' object has no attribute 'coefficient'" error message.

I solved the problem by changing the following line in the gen() method:

res = self._new_initial(1, Stream([0,1,0]))

by

res = self.term(1, 1)

The coefficient of order 1 in the series y should not be the integer 1, but the power series [1, 0, ...] in S1.

CC: axel.bacher@labri.fr @mwhansen @mantepse

Component: combinatorics

Keywords: LazyPowerSeries

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/10085

[haraldschilly]

Description changed:

--- 
+++ 
@@ -21,7 +21,7 @@
 by
 
 ```
-res = self.term(1, 1)}}}
+res = self.term(1, 1)
+```
 
-	The coefficient of order 1 in the series y should not be the integer 1, but the power series [1, 0, ...] in S1.	
-```
+The coefficient of order 1 in the series y should not be the integer 1, but the power series [1, 0, ...] in S1.	

[mantepse]

Changed keywords from none to LazyPowerSeries

[mwhansen]

comment:5

A fix is in #15673