my $a = "AB:APPLE:BOY:ZOO:ZOOM";
my $b = "APPLE:ZOO";
my $c = "BOY: GIRL";

isSubset($b, $a) returns 1 # $b is a "subset" of $a.  
isSubset($c, $a) returns 0 # $c is not a "subset" of $a.