sub intersect{
@z{@x}=@x;0+grep$z{$_},@y
#        1         2
#234567890123456789012345
}

##</code><code>##




sub intersect_dupes{
@a{@x}=@x;@b{@y}=@y;0+grep$a{$_},keys%b
#        1         2         3
#23456789012345678901234567890123456789
}