In _38 Basic Joseki_, Kosugi & Davies remark in this position:

    $$c
    $$ --------------------
    $$ -. . . . . . . . . .
    $$ -. . . . . . . . . .
    $$ -. . 1 . . O . . . .
    $$ -. . . X . a . . . X
    $$ -. . . 3 2 6 . . . .
    $$ -. . O 4 5 . . . . .
    $$ -. . . . 7 . . . . .
    $$ -. . . . . . . . . .
    $$ -. . . . . . . . . .
    $$ -. . . X . . . . . ,

that if White blocks at **2**, Black will push and cut with **3** and **5** _or **3** and **a**_.

I cannot see how one is meant to cut with **3** and **a** in this situation.
I have not found this in _Ishida_, or on Josekipedia (though someone has asked [a question about **a**](http://www.josekipedia.com/#path:pdqfpjncqcoepepfnd)) or in Sensei’s Library; though with this severely pruned search pattern (only shaded points sought):

[![enter image description here][1]][1]

there were some matches (to which the “a” refers), but nothing useful that I could see.

## Questions
* Is this a misprint, or how is one meant to cut with **3** and **a**?
* When is this preferable?
* What continuations are there, and are they joseki?

## Follow-up
I am not sure what I can have thought (though I expected **a** to be an answer to a different White **4**, rather than achieving a different objective), but now I think I see, as [Daniel T](https://boardgames.stackexchange.com/users/22965/daniel-t) says in [his answer]( https://boardgames.stackexchange.com/a/42050/14474) that the marked white stones _are_ separated:

    $$c
    $$ --------------------
    $$ -. . . . . . . . . .
    $$ -. . . . . . . . . .
    $$ -. . X . c W . . . .
    $$ -. . . X b B . . . X
    $$ -. . . X W d . . . .
    $$ -. . O O a . . . . .
    $$ -. . . . . . . . . .
    $$ -. . . . . . . . . .
    $$ -. . . . . . . . . .
    $$ -. . . X . . . . . ,

He shows W@**a**–B@**b**, but W **b** and **d** also seem to fail, with a shaky ladder and too many cuts respectively. I still do not see when this is good; maybe the issue is which 6-3 stone B wants to separate 5-5 from, but he could just push **3** in the other direction.
  [1]: https://i.stack.imgur.com/LaEg1.png