Kungfu: Tesuji is a skillful play, and sente is a move which your opponent should/must respond to. So a sente getting Tesuji is merely one of the most important points on the board.
An example, if there are three game winning plays available, playing those moves are all sente and tesuji, regardless of what is actually going on.. since any of those three moves, regardless if it's the worst one, will win the game if the opponent does not respond. Another comment on what Bill said, if I may, a tenuki which is sente and which retains sente is a sente getting tesuji, I agree.
With all that in mind, should White play a or b?
If White plays at a, then a move at b is necessary. But if White plays at b, then any move by Black on the left can be ignored and sente can be stolen. Furthermore, if Black plays c or d later, should White respond? I probably wouldn't respond after White had played b in response to Black's original hane. So is White b a sente getting tesuji?
Maybe consider that you should give up a stone to retain (or possibly steal) sente.
xela: Um, white a, black e, white b, black tenuki, white c and the corner is dead? I really think a is sente here.
Charles Matthews White at b might be correct here - but I'm not sure what is being argued, really.
Moved from sente getting tesuji