my @isec;
my @b;

(@b, @isec) = ArrayFunctions(\@ArrayA, \@ArrayB, \@b, \@isec);

sub ArrayFunctions {
    my ($a_ref, $b_ref, $b, $isec) = @_;
    my @a = @$a_ref;
    my @b = @$b_ref;
    my %Aseen = map {$_ => undef} @a;
    my %Bseen = map {$_ => undef} @b;
#.......... Other Code .....
}