3-4 point high approach, three-space high pincer
The three-space pincers against a high approach are very rare. In fact, this is almost never played in professional games (25 occurrences in 150,000 games); the low pincer at a is more common, despite not rating a mention in Ishida. Both positions (with
as in the diagram or at a) can arise by a different move order, from white invading against the high or low Chinese opening.
When is the chosen pincer here, White (in pro games) as often as not ignores it (see 3-4 point high approach three-space high pincer, tenuki). When White does reply here, White at b is most commonly played; after that, White at c.