Complement

[blegat]

I discussed with Oscar during JuMP-dev call this evening. He mentioned this issue:
jump-dev/MathOptInterface.jl#2463
He said that what PATH and Knitro need match the JuMP interface so if you do something like

@variable(model, 0 <= x <= 1)
@constraint(model, ... complements x >= 0)

with AMPL then it will have to transform the upper bound constraint x <= 1 into an affine constraint 1x + 0 <= 1.
@frapac so in the example you showed, you can just moved the upper bound constraint in a separate @constraint.