S i , k   = ∑ l  | F i  ∩ G l  |   | F k  ∩ G l  |       ( 11  )    MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8akY=wiFfYdH8Gipec8Eeeu0xXdbba9frFj0=OqFfea0dXdd9vqai=hGuQ8kuc9pgc9s8qqaq=dirpe0xb9q8qiLsFr0=vr0=vr0dc8meaabaqaciaacaGaaeqabaqabeGadaaakeaacqWGtbWudaWgaaWcbaGaemyAaKMaeiilaWIaem4AaSgabeaakiabg2da9maaqafabaGaeiiFaWNaemOray0aaSbaaSqaaiabdMgaPbqabaGccqGHPiYXcqWGhbWrdaWgaaWcbaGaemiBaWgabeaakiabcYha8bWcbaGaemiBaWgabeqdcqGHris5aOGaeiiFaWNaemOray0aaSbaaSqaaiabdUgaRbqabaGccqGHPiYXcqWGhbWrdaWgaaWcbaGaemiBaWgabeaakiabcYha8jaaxMaacaWLjaWaaeWaceaacqaIXaqmcqaIXaqmaiaawIcacaGLPaaaaaa@4ED6@