Ivan Detkov: I agree. The drawback of P19 vs. Q18 is it gives away an extra ko-threat for nothing. It seems like a not big deal but it is important to learn a good style early.
shiyon: being alive with no issue is always better than having to win a ko to be alive, just because the board is cut off doesn't mean the rest of the game disappears.
caranthir: There's nothing wrong with P1, since even after that it's not really a ko. After any ko threat + response + retake, we can always go back to playing Q2. If on the other hand P1M1/O3, then we take at Q2.
The take-home message for a beginner would be to recognize the oshi-tsubushi move Q18 here and as a theme in other similar situations. I think we could leave this problem as is, so that it enforces the theme; therefore, taking the ko is wrong here even though in real life ironically, it'd be totally right.
m b: Setup in top right corner.
I go P19. Oponent can't go O19 or Q18. Does any other move, but can't capture anything. I go Q18 and am safe.
What am I missing?
shiyon:
M. Szpura:
See above. It doesn't matter.