Find the fillet solution at a specific locus.

Input parameters:

1. Cr → Curve to fillet.
2. Lc → Curve locus for fillet.
3. Rd → Fillet radius.

Output parameters:

1. Ar → Fillet arc.
2. La → Locus on the curve for the arc start.
3. Lb → Locus on the curve for the arc end.