See one of the above posts for details, but the idea is to find the oldest file in your home directory tree, and tell its story.
I found these:
avl.c starts like this:
*** avl.c --
*** The AVL height-balanced tree abstraction.
*** Six functions are defined:
*** returns an empty avl tree.
*** addnode(tree, key, data, compare)
*** Adds a new node to the tree given.
*** node = findnode(tree, key, compare)
*** Finds the node in the tree.
*** modnode(tree, key, data, compare)
*** Modify an existing node.
*** im = startiter(tree)
*** Starts an iteration over the nodes, returning an
*** iteration map.
*** im = nextnode(tree, im, &node)
*** Returns the new map, and writes a pointer to the next
*** size = avlsize(tree)
*** Returns the number of nodes in the tree.
*** N.Batchelder, 5/7/85.
*** Adapted 1/13/85.
Clearly this would simply be a dictionary today, but I had to go and write an entire data structure to be able to store the symbol table for PSCom. The adapted date must be a typo, it was adapted 1/13/86, based on the comment in avl.h If it was truly begun in May of 1985, then it was originally part of a different project, perhaps a PostScript-like language implementation I was working on while at Penn.
One odd feature of PSCom: when shortening identifiers, you could choose the set of characters that would be used. PostScript has very lenient rules regarding allowable characters in identifiers, so you could use -_= as the set to choose from, and end up with a final file that looked like hardware timing diagrams, or ,.:;’ which would be indistinguishable from chicken scratch.
One thing about the code that strikes me now: I wrote a lot of comments back then! I should get back into that habit...