1 birulami Posts: 130 Hi, recently I stumbled across the question whether for finite sets [itex]A,B[/itex] the function [tex]d(A,B):=|A\cup B| - |A\cap B|[/itex] is a metric ? Trivially, [itex]d(A,A)=0[/itex] and of course [itex]d[/itex] is symmetric, but how about the triangle inequality? Does it hold? Harald.   birulami View Public Profile Find