Opened 9 years ago

Closed 6 years ago

No coercion map with quotients of ring quotients

Reported by: Owned by: tscrim tscrim major sage-6.4 coercion ideal, quotient, coercion boerner, saraedum Travis Scrimshaw Michel Boerner, Julian Rueth N/A d935124 d93512419089b35d11d0c05a3533a80eb41a5790

Description

If you take the quotient ring of a quotient ring, I would expect there to be a coercion map corresponding to the natural surjection. However this does not occur:

```sage: R.<x,y> = PolynomialRing(QQ)
sage: S = R.quotient_ring(x^2+y^2)
sage: S
Quotient of Multivariate Polynomial Ring in x, y over Rational Field by the ideal (x^2 + y^2)
sage: S.has_coerce_map_from(R)
True
sage: T = S.quotient_ring(x^3 - y)
sage: T
Quotient of Multivariate Polynomial Ring in x, y over Rational Field by the ideal (-x*y^2 - y, x^2 + y^2)
sage: T.has_coerce_map_from(R)
True
sage: T.has_coerce_map_from(S) # this should be true
False
```

I suspect the following does not occur either (and is where the problem lies). If an ideal `I` is contained in an ideal `J`, there is not a coercion from `R/I -> R/J`.

comment:1 Changed 8 years ago by jdemeyer

• Milestone changed from sage-5.11 to sage-5.12

comment:2 Changed 7 years ago by vbraun_spam

• Milestone changed from sage-6.1 to sage-6.2

comment:3 Changed 7 years ago by vbraun_spam

• Milestone changed from sage-6.2 to sage-6.3

comment:4 Changed 7 years ago by vbraun_spam

• Milestone changed from sage-6.3 to sage-6.4

comment:5 Changed 7 years ago by tscrim

• Authors set to Travis Scrimshaw
• Branch set to public/coercion/between_quotient_rings-13682
• Commit set to d93512419089b35d11d0c05a3533a80eb41a5790
• Status changed from new to needs_review

We have to do an ideal membership test, which means computing Groebner bases. However it now returns the correct (or at least more intuitive) answer. Needs review.

New commits:

 ​d935124 `Expanded coercions between quotient rings.`

comment:7 Changed 6 years ago by boerner

• Reviewers set to Michel Boerner, Julian Rueth
• Status changed from needs_review to positive_review

comment:8 Changed 6 years ago by tscrim

Thanks for the review!

comment:9 Changed 6 years ago by vbraun

• Branch changed from public/coercion/between_quotient_rings-13682 to d93512419089b35d11d0c05a3533a80eb41a5790
• Resolution set to fixed
• Status changed from positive_review to closed
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