The Generic Existence of a Core for q-Rules

A q-rule is where a winning coalition has q or more of the n voters. An important issue is to understand when, generically, core points exist; that is, to determine when the core exists in other than highly contrived settings. As known, the answer depends upon the dimension of issue space. McKelvey and Schoeld found bounds on these dimensions, but Banks found a subtle, critical error in their proofs. The sharp dimensional values along with results about the structure of the core are derived. These values can be identied with the number of issues needed to lure previously supporting voters into a new coalition.