3-3 point shoulderhit - which way to push

Diagram 1  

Should Black play at a or at b?

It depends on the positions on the upper side and on the right side. Black wants to make the keima slide at move 3 be effective.

For example

Diagram 2  

When the stone is on the board, works beautifully to undermine White's position.

On the other hand

Diagram 3  

This way White can play instead of c, making use of .

I remember a game many years ago between Ishida and Nie Weiping in which a shoulder hit on a 3-3 stone occurred very early in the game, at a point when there were no stones on the two sides adjacent to the 3-3 point, and much of the subsequent opening maneuvers were focussed on making the keima slide a good or bad choice.

Charles Yes, there have been dozens of pro games of this kind, with played as a shoulderhit and probe.

Fuseki pattern with nirensei  

For example when Black plays nirensei with here, it signifies that works better with a black stone at a.

A rare fuseki pattern is at 3-3, shoulderhit: even more so, White is trying to wrong-foot Black. There is a classic game Sakata-Go Seigen like this, from 1963, just on the cusp when Sakata was taking over as the top player.