Unconcerned groups and the majority rule

When preferences are defined over two alternatives, the (relative) majority rule is characterized in terms of the four axioms U, P, I, and G. U is unanimity. P is the condition that the union of two unconcerned (that is, indifferent) groups of individuals creates an unconcerned group. I asserts that the preferences of the individuals of an unconcerned group can be cancelled out without altering the result. G states that, for any sufficiently small group G that is not unconcerned and for any group H with the same size as G but without members in common with G, it is possible to make the union of G and H unconcerned.