I have some litters : a b d thanks 1 2 2 4 2 4 4 8 item #1 item #2 item #3 2 4 Test #1 : a b c d 1 2 3 4 5 1 2 3 4 5 item #1 item #2 item #3 Test #2 : <#1 -------------- > <#2 ----------------- > <#2 ----------------- > <#3 ----------------- > <#3 ----------------- > <#1 -------------- > <#2 ----------------- > <#2 ----------------- > <#3 ----------------- > <#3 ----------------- > Test #3 : 1 3 5 7 9 h e l l o Test #4 : 120