[Help-glpk] MIP problems

[ΤΑΣΣΟΠΟΥΛΟΣ ΙΩΑΝΝΗΣ]

Hi to everyone,

I have been aware that MIP problems are NP-Complete or even NP-Hard.

Does any one know a reference (perhaps a published paper) in which it is proven that MIP problems are NP- Complete or NP- Hard?

Thank you very much for your time and for any answer.

Ioannis Tassopoulos