Problem diagram.
White to play in the upper right.

Source:
American Go Journal, Vol. 22, No. 2, pp. 29-30
Keshi and Uchikomi, Kaoru Iwamoto 9 dan

Solution follows    (or click here to download SGF)

A mistake.
With 1, White fortifies his own position in the lower right, but with 2, Black also fortifies. White has lost the chance to invade.

Inadvisable.
White 1 is the standard erasing point for this type of formation, but only larger Black frameworks require such a light erasing move. Black 4 defends the upper right, while White must make another move to make shape.

For example, White can block with 5, but now Black can easily invade at 6 with such strong support from above.

Correct.
A White invasion at 1 is called for. The best response is Black 2, which intends to indirectly consolidate the corner by pushing White in that direction. White 3 is the only move. White's 5, 7, and 9 moves may seem tactless, but are proper here. White has a flexible shape. For example, if Black jumps toward the bottom with 10, White can defend and then further extend to make contact with his upper side stone. White has accomplished his objectives.

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