2C-two-columns is an interactive autoloaded compiled Lisp function in `two-column.el'.

It is bound to <f2> <f2>, <f2> 2, C-x 6 <f2>, C-x 6 2.

(2C-two-columns &optional BUFFER)

Split current window vertically for two-column editing.
When called the first time, associates a buffer with the current
buffer in two-column minor mode (use C-h m once in the mode,
for details.). It runs `2C-other-buffer-hook' in the new buffer.
When called again, restores the screen layout with the current buffer
first and the associated buffer to its right.