Polygon:
->new( Point p1, Point p2, ... );
->has_inside( Point p );  # return true/false
->get_outside_point();    # return Point outside the polygon
->first_line();           # return 'line 1' - reset counter
->next_line();            # return next_line, incr counter
                          # undef if no more

Line:
->new( Point x, Point y );
->intersects( Line l );   # return true/false
# Is this what you mean by 'same_line'?
->equals( Line l );       # return true/false