http://0-delivery.acm.org.library.vu.edu.au/10.1145/1070000/1066838/p706-aleksy.pdf?ip=140.159.34.46&acc=ACTIVE%20SERVICE&key=C2716FEBFA981EF1AD54CD80235F77C5DBFB825C1852FBF1&CFID=207768726&CFTOKEN=45530793&__acm__=1366601149_46ea5a4b0c379d103dbe1b85acb67