XP1XP2XP3  ... =EPX 11x x 33 .. . 22 and then P is the

distribution function of objects into parcels (pi 1pz2pa3•••), the distributions being such as to have the specification (sils,2°2s3a...) . Multiplying out P so as to exhibit it as a sum of monomials, we get a result XP1"1XP2"2XP"3 3 ... = EEB(xt11Xt22 .. . 3 el a2 a3 indicating that for distributions of specification (s°ls, 2s83...) there are 0 ways of distributing n objects denoted by (a11x22As3...) amongst n parcels denoted by (pilp22p;3...), one object in each parcel . Now observe that as before we may interchange parcel and object, and that this operation leaves the specification of the distribution unchanged . Hence the number of distributions must be the same, and if XPt"lxP"22Px"3a ... =...+8(~11~22~a3...)xslx 12xe3... j ...