|Table of diagrams
Dia 2 (White 11 at ''a'')
A general comment.
Dia 2 (White 11 at ''a'')
How to develop?
Where this all starts
Floris: Therefore I usually find it good to first approach the upper right, and then invade, making Black overconcentrated: if he plays along, that is.
Patrick Traill: What is the premise of therefore? Some context needed!
aLegendWai: It is my little opinion. Correct me if wrong.
is not good to W. Playing a diagonal play 1 line lower than the opponent's stone along the edge is generally bad. Also a and b are not equal good points. Now B should play at b. (Playing a gives the chance for W to destroy the upper right side. Hardly good in this case).
So if Black b, White a, then Black c is a good hane to press W severely.
may try to play at d if it wishes to be safe (?). at b/e is possible in some cases but probably not in this case. Black is too strong here. I deem if the 3 B stones on the upper right does not safely guard the territories around, b/e can be good, right?
Anyway, I think it is a hard time for W. Maybe shouldn't invade too deep in the first place. 
Mef: Much of this has already been discussed farther down on this page.
Actually, Black made a (small) mistake (not wrong in all situations) somewhere, can you spot it?
Out of all the other pincers puts the most pressure on White. The continuation up to is most usual, except Black will have a huge advantage in the coming fight as White has two weak groups. Notice the black move at tengen is a ladder breaker here and without it is much less severe (makes the cut at impossible).
tderz Above diagram follows the same concept as Go Seigen's advice to play - the usually disliked (despised?; we usually teach kyus not to play like this, but to go out into the center ) here - because Black has a strong environment, hence wants and needs to fight for maximum efficiency.
 Go lives up by the exceptions!
Black has the upper hand in any subsequent fighting in this quarter of the board. is better than
Yes, is the very move, critizised in  !
in this diagram looks bad to me. Black happily takes the opportunity to strengthen herself with , then attacks White's shape with (looks better than a). Sure, White will live, but Black becomes thick. BobMcGuigan-- See Angle play after diagonal attachment
tderz Appeal to authority - if it has been played by professionals? (ok, logically irrelevant, but rhetorically quite strong, ^^)
In the diagram that you consider 'better', I have the feeling that is a serious overplay.
 tderz: saving pivotal cutting stones is
common sense within the context of the fundamentals of Go.
It could only be bad if there was something (even) better.
Furthermore, White is left with cutting point b and has a hard time to make eye shape - if any. While (ok, more seriously: after) white has taken care of her group), Black has sente to do whatever he likes in the white spheres of influence.
In conclusion, the sequence 3-5-7-9 rather gives the impression as if a loose ladder or geta was started - which in the end does not work (ouch!).
If anything wrong with the cutting stone in the diagram  in question (which might be possible after all) - then, at least, this diagram here does not seem to prove it (at all).
Rather , these moves 3-5-7-9 give a blunt and unimaginative impression. Many lose-looking, vague moves would have much more objective potential than this sequence (my opinion and cf. ).
I don't agree that White is left with two weak groups - Black is so strong in this environment to start with, that White should have no qualms about sacrificing one of them. Here you see one possible continuation.
Here is another possibility. Black might seem to be doing well, but White a-Black b-White c, killing the corner is hanging above him, like the sword of Damocles. .
Charles Like Andre, I have difficulty accepting these statements.
So I doubt that is really a mistake.
aLegendWai: I would like to know why the exchange and is needed. Is it good? (Say why not play at a instead?)
Also, I don't like the angle play for White here except in a different context. See discussion at Angle play after diagonal attachment.
unkx80: A general comment:
For players who are uncomfortable playing at Black a and allow an invasion at White b, he or she can consider playing at or c instead. Then at a later move, Black can play at a if White has not already played in the vicinity.
Yes White indeed lives, but tengen stone really doesn't do much at the moment and Black is fairly overconcentrated in the top right. I suppose a move at a would make it easier to make territory with the tengen stone but then White can take a remaining big point on the board.
I cannot call this a good result for White. Black is whistling while solidifying tons of territory as White is fleeing for life.
I think is a bit mild, maybe at a is better to put more pressure on White. Also, after the sequence you show up here, I think Black b is a very severe follow-up (this would have been even more severe if was at a, but then White wouldn't play ). Sure Black's corner isn't alive yet, but he should first worry about making profit from attacking the two white groups before worrying about the status of his corner.
tderz I do not look at all in detail into this matter now (it's late). I do not want to say rightout that is slack. However, my flash impression is that moves like c or (at ) are very often tesuji (one just have to chose the side). Also a move at a takes at least liberties (ok, also of the own stones, but B is fighting a home game here) and enables much better moves as b. My 1st choice (or thoughts) would be to decide here on either c or .
Charles You know, Floris, we can't just accept that Guo is your teacher, she tells you things, you tell us, and we have to agree!
OK, maybe I now start to understand. Given this position, the pros just don't add the tengen stone (Black at the circled point).
The widest path here is , then to invade. Perhaps what Floris is telling us is an answer to a 'what if?' question. What if Black does make a four star points box formation? That's not so common in pro play - tengen isn't so easy to use. But without any examples for the 'pro invasion' diagram, what can one say?
If I can tentatively reconstruct the lesson:
Black's use of tengen here isn't favoured by pros. But amateurs often play it. If White enters a box formation that isn't really well constructed, maybe immediate life might be enough (showing why Black's strategy with tengen wasn't so good). Therefore Black must play a more aggressive way - the requirements of the position dictate it.
I'll accept that the angle play might be appropriate here, then. There is another way to play, also needing consideration. The general technique has been called digging in?,
Therefore, going back to the starting diagram, we could call here questionable.
It probably isn't the case that is the biggest point. Black must make sure this stone is used to fight.
White has played a strong group plan on the right side. This isn't a case of making Black over-concentrated, though.
I see that this position has occurred in a couple of pro games from China. In both cases Black played at a instead of .