White 4 is an enclosure

A rare idea for opening the game is for White to play and as a corner enclosure, thus allowing Black three corners. It was tried as an experiment by Kubomatsu, and probably on a few other occasions by strong players.

Gu Li made a 3563 enclosure with and in a game 2001-09-14.

Naganuma Makoto -Takahashi Toshimitsu  

In this game between Naganuma Makoto and Takahashi Toshimitsu, the latter played and as an enclosure. White lost the game, not that there is any statistical relevance to that.