WARP and combinatorial choice

For combinatorial choice problems, I show that the Irrelevance of Rejected Items condition is equivalent to the Weak Axiom of Revealed Preference (WARP), and is necessary and sufficient for the existence of a complete, reflexive and antisymmetric rationalization of a combinatorial choice function. I also show the equivalence of WARP to path independence and to other classical choice conditions when the choice domain is combinatorial.