Fix a bug in sorting RealSets

[yuan-zhou]

Find a bug:

sage: RealSet((0, 1),[1, 1],(1, 2))
(0, 1) + [1, 2)

should return

(0, 2)

This can be fixed by a modification in RealInterval.__cmp__: when comparing two intervals with the same lower bound, put lower_closed before lower_open. i.e. [a, b] < (a, c].

CC: @tscrim @vbraun

Component: calculus

Keywords: real_set

Author: Yuan Zhou

Branch/Commit: 97e50b5

Reviewer: Ralf Stephan

Issue created by migration from https://trac.sagemath.org/ticket/17714

[yuan-zhou]

Changed keywords from none to real_set

[yuan-zhou]

Author: Yuan Zhou

[rwst]

comment:3

Thanks. Please always include a doctest, and set needs review. I will do it this time and do the review, as well.

[rwst]

Changed branch from u/yzh/test_branch to u/rws/test_branch

[rwst]

Reviewer: Ralf Stephan

[rwst]

Changed commit from 20cbe14 to 97e50b5

[rwst]

comment:5

This looks fine, tests OK with make ptestlong.

---

New commits:

97e50b5

17714 reviewer's patch: add doctest, cosmetics

[vbraun]

Changed branch from u/rws/test_branch to 97e50b5