I think I don't understand how constraints work.

Situation is as follows:

There are 9 constraints:

2 fix the 2 points on the arc

5 coincidences (the 2 extremes of the arc with the 2 extremes of the lines, the other 2 extremes of the lines with the origin, and the center of the arc with the origin)

2 symmetries (the 2 extremes of the arc with the y axis, and the 2 points on the arc with the y axis)

In this situation I can't move anything.

There is one redundant constraint, because I don't need both points to be fixed on the arc. One point fixed and the symmetry should be enough.

Indeed, if I remove one of the constraints fixing the points on the arc, then I can move things (obviously within the limits of my constraints).

Why is that? Why is a redundant constraint preventing me from moving anything?