1≤i<)≤nT∈F,write Tii=(T\{})U{} m-8 ifj∈T,itT,andT年F, otherwise. S(F)={S(T)|T∈F} 1.lS(T)川=T and|Si(F)川=lF到 2.F intersecting Si(F)intersecting repeat applying (i,))-shifting Sis(F)for 1<i<jn eventually,F is unchanged by any Sj(F) called:F is shiftedSij (T) = ￾ Tij if j ￾ T,i ⇥￾ T, and Tij ⇥￾ F, T otherwise. 1 ￾ i<j ￾ n ⇥T ￾ F, write Tij = (T \ {j}) ⌅ {i} Sij (F) = {Sij (T) | T ￾ F} repeat applying (i, j)-shifting Sij (F) for 1 ￾ i<j ￾ n eventually, F is unchanged by any Sij (F) called: F is shifted |Sij (T)| = |T| F intersecting Sij (F) intersecting 1. and 2. |Sij (F)| = |F|