sage: P = LaurentPolynomialRing(QQ, 'a, b')
sage: Q = LaurentPolynomialRing(P, 'c, d')
sage: Q(P.0)
c

but the expected result is a as it is with polynomial rings:

sage: P = PolynomialRing(QQ, 'a, b')
sage: Q = PolynomialRing(P, 'c, d')
sage: Q(P.0)
a

2. (In some sense) more generally, conversion between certain laurent polynomial rings (e.g. isomorphic rings) fail. E.g. the following should work

sage: L.<a, b, c, d> = LaurentPolynomialRing(QQ)
sage: M = LaurentPolynomialRing(QQ, 'c, d')
sage: Mc, Md = M.gens()
sage: N = LaurentPolynomialRing(M, 'a, b')
sage: Na, Nb = N.gens()
sage: M(c/d)
sage: N(a*b/c/d)
sage: N(c/d)
sage: L(Mc)
sage: L(Nb)

3. As needed to fix the above, a method is_constant, as well as methods for the conversions of constant laurent polynomials are to be implemented.

Depends on #21833

CC: @cheuberg

Component: algebra

Author: Daniel Krenn

Branch/Commit: 65e2fc5

Reviewer: Frédéric Chapoton, Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/21855