Any time you want to know if one value is in a set of others, you probably want a hash. Convert @b to a hash (with the values as keys), then loop on @a, checking if the values exist in %b. Here's an example:

    my @a = qw(one two three four);
    my @b = qw(two four);
    my %b;
    @b{ @b } = (1)x@b; # one of many ways to create the hash

    for (@a) {
      unless ($b{$_}) { print "$_ is not in \@b\n" }
    }
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