A central result in the theory of integer optimization states that a system of linear diophantine equations Ax = b has no integral solution if and only if there exists a vector in the dual lattice, y T A integral such that y T b is fractional. We extend this result to systems that both have equations and inequalities {Ax = b, Cx d}. We show that a certificate of integral infeasibility is a linear system with rank(C) variables containing no integral point.
Andersen, K., Louveaux, Q., & Weismantel, R. (2007). Integral Farkas type lemmas for systems with equalities and inequalities (CORE Discussion Papers 2007/51). https://hdl.handle.net/2078.5/129300