?

This procedure is used with no arguments only in interactive mode to display the content of the current history. The history is keeping the last 20 expressions entered in interactive mode.

Example:

[1] (define a 1)
a
[2] (+ a 1)
2
[3] (?)

   [1]: (define a 1)
   [2]: (+ a 1)
   [3]: (?)
ok
[4]