"The Calculus of Friendship" by Steven Strogatz

In The Calculus of Friendship: What a Teacher and a Student Learned about Life While Corresponding about Math, Cornell University math Professor Steven Strogatz shares some of the correspondence he shared over several decades with his high school calculus teacher, Don Joffray.

The book is short, and a quick read if you don’t try to follow too closely the mathematics the two correspondents toss at each other. The two men reverse roles over time — originally Strogatz was the student, but in time he becomes the teacher. Along the way, Strogatz and “Joff” share the joy of being challenged by interesting math problems. But their interaction, while lively, is also frequently sporadic. Neither man (particularly Strogatz) seems comfortable in becoming a friend who shares more than just a love of math and the highlights of day-to-day life. It is only as the two men grow older that they bridge the gap and communicate their more personal feelings. Both men suffered the kinds of personal losses common to most of humankind, but they each failed to share their vulnerability and need for emotional support. One can appreciate the special bond between these two men, even as one can imagine what a deeper relationship might have brought them.

Yes, mathematics is key to this story. But the real theme is friendship, what brings us together, and what we may miss out on by not opening up on a deeper level.