Unusual enclosures and tenuki variations
Charles A bad tenuki, though, since Black a is strong: see 3-5 point low approach one-space low pincer, tenuki. See 3563 enclosure for White attacking at a instead, the apparent vital point.
But the previous diagram shows the usual invasion point.
In most of these cases of unusual enclosures, if White were to invade the black formation at a natural point it would result in a position equivalent to White having played tenuki against a pincer.