we have to deal with what remained from #12091. At least, report errors for the inputs like the following:

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

which even with #12091 are incorrectly processed

sage: b[0] <= 555*b[1] >= 2
2 <= x_0 <= 555*x_1
sage: b[0] <= 555*b[1] == 2
555*x_1 == 2

Depends on #14540

CC: @vbraun @ppurka @nathanncohen

Component: linear programming

Reviewer: Jeroen Demeyer

Issue created by migration from https://trac.sagemath.org/ticket/13696