Surjections U=[ml→[m A:=[n→([m]\{i}) Ag=UAr=∩Ai=[m]→(m\I) i∈I |A=(m-|I)” U-UA=∑(-1)川14 IC[m] -0m-0°--1m(） IC(m] k=1Surjections U = [n] ￾ [m] Ai = [n] ￾ ([m] \ {i}) AI = ￾ i￾I A￾ = U Ai = [n] ￾ ([m] \ I) |AI | = (m ￾ |I|) n = ⇤ m k=1 (￾1)m￾k ￾m k ⇥ kn = ￾ I￾[m] (￾1)|I| (m ￾ |I|) n ￾ ￾ ￾ ￾ ￾ ￾ U ￾ ⇥ i￾[m] Ai ￾ ￾ ￾ ￾ ￾ ￾ = ￾ I￾[m] (￾1)|I| |AI |