For S = {a, b, c}, consider the function
f(x) = (1 + ax)( 1 + bx)( 1 + cx)
= 1 + ax + bx + cx + abx2 + acx2
+ bcx2 + abcx3.
Here, in f(x)
• The coefficient of x° is 1 -for the subset 0 of S.
• The coefficient of xl is a + b + c - for the subsets {a}, {b}, and {c} of S.
• The coefficient of x2 is ab + ac + bc - for the subsets {a, b}, {a, c}, and {b, c] of S.