One thing to note about groups is that it is not always the case that a â cents b = b â cents a for every a and b in the group . If a group does have the property that a â cents b = b â cents a we call it an abelian group . For example , repeated applications of the associativity axiom show that the unambiguity of a â cents b â cents c = ( a â cents b ) â cents c = a â cents ( b â cents c ) generalizes to more than three factors .