Robert Bilinski proposed this problem in the April 2006 issue of *Crux Mathematicorum*. On square *ABCD*, two equilateral triangles are constructed, *ABE* internally and *BCF* externally, as shown. Prove that *D*, *E*, and *F* are collinear.

*Crux Mathematicorum*. On square *ABCD*, two equilateral triangles are constructed, *ABE* internally and *BCF* externally, as shown. Prove that *D*, *E*, and *F* are collinear.