sub intersects {
  my ($self, $arg1, $arg2) = @_;
  unless ( 
    ($self->_is_point($arg1) or $self->_is_line($arg1))
      &&
    ($self->_is_point($arg2) or $self->_is_line($arg2))
  ) {
    die "Bad args";
  }

  if ($arg1->isa('point') and $arg2->isa('point')) {
    return $arg1->equals($arg2);
  }
  elsif ($arg1->isa('point') and $arg2->isa('line')) {
    return $self->_lp_intersect($arg1, $arg2);
  }
  elsif ($arg1->isa('line') and $arg2->isa('point')) {
    return $self->_lp_intersect($arg2, $arg1);
  }
  elsif ($arg1->isa('line') and $arg2->isa('line')) {
    return $self->_line_intersect($arg1, $arg2);
  }
}