Fix chaining of MILP constraints

[nathanncohen]

sage: p = MixedIntegerLinearProgram()
sage: b = p.new_variable()
sage: int(1) <= b[0] <= int(2)
x_0 <= 2

sage: p = MixedIntegerLinearProgram()
sage: b = p.new_variable()
sage: float(0) <= b[0] <= int(1) <= b[1] <= float(2)
1 <= x_1 <= 2

sage: p = MixedIntegerLinearProgram()
sage: b = p.new_variable()
sage: b[0] <= 555*b[1] >= 2
2 <= x_0 <= 555*x_1

This can never work due to the way Python handles chained comparisons:

sage: p = MixedIntegerLinearProgram()
sage: b = p.new_variable()
sage: b[0] <= 3 <= 4
True

Depends on #20478

CC: @vbraun @dimpase @mkoeppe @videlec @tscrim

Component: linear programming

Author: Jeroen Demeyer

Branch/Commit: 96e133e

Reviewer: Matthias Koeppe, Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/14540

[dimpase]

comment:1

In a script - do you mean a Python script, not Sage script, right?

[nathanncohen]

comment:2

Well, in any script that does not wrap integers with Integer(). So a .py that you load with %runfile is ok !

Nathann

[dimpase]

comment:3

Replying to @nathanncohen:

Well, in any script that does not wrap integers with Integer(). So a .py that you load with %runfile is ok !

Nathann

and it's not only int, but float, too, that gives this problem.