sub easy
{
    my $a= shift;      # array ref
    my $b= shift;      # array ref
    my @diff= ( 1, 0, -1, 0, -1 );
    traverse_sequences( $a, $b, {
        MATCH => sub {
            my( $aEnd, $bEnd )= @_;
            $_++ for my( $aTop, $bTop )= @diff[ 2-5, 4-5 ];
            if(  $aTop < $aEnd  ||  $bTop < $bEnd  ) {
                push @diff, 0, $aTop, $aEnd-1, $bTop, $bEnd-1,
                            1, $aEnd, $aEnd,   $bEnd, $bEnd;
            } else {
                @diff[ 2-5, 4-5 ]= ( $aEnd, $bEnd );
            }
        },
    }, @_ );
    my( $aEnd, $bEnd )= ( 0+@$a, 0+@$b );
    $_++ for my( $aTop, $bTop )= @diff[ 2-5, 4-5 ];
    if(  $aTop < $aEnd  ||  $bTop < $bEnd  ) {
        push @diff, 0, $aTop, $aEnd-1, $bTop, $bEnd-1;
    }
    splice @diff, 0, 5   if  $diff[2] < 0  &&  $diff[4] < 0;
    return wantarray ? @diff : \@diff;
}