AddASecondStoneAndSacrificeBoth/continuation

Starting position  

What is the point of black playing at a when white can capture that stone later? Let's discuss:

Options  

Let's look at three options. a, b and tenuki.

Kikashi  

If Black at here, can play tenuki. ends in gote. Later there is the alphabetized endgame.

(Of course, if black is komaster, black could respond to white a with black c. But in general, black has to draw back to b because white will have little to lose in the ko.)

Gote  

If Black does not play tenuki, he ends in gote. We can expect White a, Black b, White c in the late endgame.

(When compared with the sente diagram above, here is worth only about 9 points in gote. Before yose, this is relatively small, so tenuki is most likely a better option.)

Gote  

Black gives up the possibility of tenuki and ends up in gote anyway. In the endgame we can expect Black a White b Black c.

Tenuki  

If Black plays tenuki, can be sente.

The third part may be explained elsewhere already