Create an ellipse out of focal points and a coincident point.

Input parameters:

1. Pl → Optional plane for ellipse. If omitted, the three points define the plane.
2. F1 → First focal point of ellipse.
3. F2 → Second focal point of ellipse.
4. Pc → Point coincident with ellipse.

Output parameters:

1. El → Ellipse from foci and coincidence.