sum(v,w,f) yields the sum of the results obtained by applying f to each of the pairs (i,j) of elements from the lists or sequences v and w, which should be of the same length.
i1 : R = ZZ[x,y,z];
i2 : sum({2,3,4},{x,y,z},(i,j)->j^i)
4 3 2
o2 = z + y + x
o2 : R