Please enable Java for an interactive construction (with Cinderella).

One can slightly move the yellow point and see what happens.
This is an arrangement of 15 lines on real projective plane with disconnected
moduli space. The moduli space is parametrised by the position of point "P"
on line "a".The arrangements are combinatorially the same when "P" is located slightly to the right or left relatively
to the red point. But it degenerates if "P" is equal to the red point. In this situation
the triangle formed by lines "a", "r" , "o" degenerates to point.
Such an effects are usually very subtle and it is difficult to scale the picture to make it visionable.
In our Cinderella mechanism the critical triangle is homotetically enlarged to the red one.
Also badly visionable triangle "r", "k" , "n" is enlarged to the green one.

Created with Cinderella