The regular division of the plane into congruent figures evoking an association in the observer with a familiar natural object is one of these hobbies or problems...I have embarked on this geometric problem again and again over the years, trying to throw light on different aspects each time. I cannot imagine what my life would be like if this problem had never occurred to me; one might say that I am head over heels in love with it, and I still don't know why.
