Infinite recursion when taking a resultant over a complicated base ring

[pjbruin]

The following resultant computation used to lead to an infinite recursion before #17974 (merged in 6.7.beta0):

sage: A.<a,c> = Frac(PolynomialRing(QQ,'a,c'))
sage: B.<d,e> = PolynomialRing(A,'d,e')
sage: R.<x> = PolynomialRing(B,'x')
sage: (a*d*x^2+a+e+1).resultant(-4*c^2*x+1)
Traceback (most recent call last):
...
RuntimeError: maximum recursion depth exceeded while calling a Python object

Although this particular bug is now fixed, the doctest and the shortcut added by this ticket may still be useful.

Component: algebra

Keywords: infinite recursion polynomial resultant

Author: Peter Bruin

Branch/Commit: 0983972

Reviewer: Vincent Delecroix

Issue created by migration from https://trac.sagemath.org/ticket/17971

[pjbruin]

Author: Peter Bruin

[pjbruin]

Commit: da8ddc1

[pjbruin]

Branch: u/pbruin/17971-infinite_recursion

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

0983972

Trac 17971: fix infinite recursion in FractionField_generic._element_constructor_()

[sagetrac-git]

Changed commit from da8ddc1 to 0983972

[videlec]

Reviewer: Vincent Delecroix

[vbraun]

Changed branch from u/pbruin/17971-infinite_recursion to 0983972