My question pertains to outside contact on a 3-4 approach to a 5-4 stone.
The only response for White given in Essential Joseki is at a. However, most players my level (now 5k* IGS) don't seem to know that that's the right way to play. At 6k*, they used to usually play at b, much to my sadistic delight (see Six Kyu Noseki for why this is a terrible move). However, at 5k*, I've started seeing c, to which I'm not quite sure how to answer.
Simply playing at a occurs to me as a possibility, but with the inevitable White answer at d, Black has played into a Hane at the Head of Two Stones, so that's probably not so good. Instead, I usually play at b, in order to confuse my opponent as much as he confused me. From there, things inevitably get complicated, and sometimes it goes my way, sometimes not. I also thought about the hane at c.
So, basically, the question is, how should I be answering the marked White stone? a, b, c, or something else entirely?