Combine a pincer with an extension
A pincer is a severe move, preventing an enemy approach stone to make a base. An extension maps out a sphere of influence making it more difficult for the opponent to approach. Combining a pincer with an extension obviously is interesting.
Bill: is a bit far to be considered an extension, I think. It leaves room for a wariuchi at a, not to mention other invasions.
Charles Matthews I think you can't have a 'nine-space extension', because a wedge in it doesn't constitute an invasion. But I have been told (and believed) that 'eight-space extension' makes sense, as the maximum.
Dieter; Yes I was aware of the example not being optimal. Please replace with a better example and I'll try the same.
Charles In this case looks efficient as a pincer on , and an extension from the formation.
dnerra And here an example where the extension from the left is pretty solid. Probably White should consider playing at a instead. In that case, a pincer would make Black overconcentrated.
Charles Isn't almost too close to Black's group anyway? What about at b? In fact Segoe played at c instead, against Go Seigen - this side formation is rare in pro play. But White more often plays the approach at d.
This from 1995-11-09 is an example of the comparable thing, just with less thickness for Black: extends from while pincering .
Bill: What I was taught was that 5 spaces is the maximum for an extension, because, for instance:
Charles Shusaku played here in one of his games. It's interesting to go back over some of these old ideas. In many cases they do relate to nineteenth-century go.