TherapieGo: I agree with smontiel's comment to add the R1 move as a good answer at the end, if you don't want to add it then don't continue the problem by making the opponent play T1 as it takes away a ko threat for nothing as you pointed out, if it works for one it works for the other.
caranthir: If you look at it, most of the resisting moves in almost all tsumego are objectively "bad" moves; losing points, wasting ko threats etc. Thus in this context there's nothing special in T19. The preceding moves R18 and O19 in that same sequence are also bad moves and the opponent should rather play elsewhere. They are there in the tsumego, like resisting moves do, to test the solver that they understood their moves correctly and to demonstrate the features of the shape. Its a different issue altogether that the *solver* is demanded to come up with the best moves, even regarding endgame and ko threats and such, as is often the case in the intermediate and harder collections. It's the solver who learns.
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A more general moral of the story: resisting moves in tsumego are not to be emulated (unless sometimes for practical purposes, when there are no other winning chances in a game but to try to play bad moves in order to possibly induce even worse moves), but just to test the learner.
If you look at it, most of the resisting moves in almost all tsumego are objectively "bad" moves; losing points, wasting ko threats etc. Thus in this context there's nothing special in T19. The preceding moves R18 and O19 in that same sequence are also bad moves and the opponent should rather play elsewhere. They are there in the tsumego, like resisting moves do, to test the solver that they understood their moves correctly and to demonstrate the features of the shape. Its a different issue altogether that the *solver* is demanded to come up with the best moves, even regarding endgame and ko threats and such, as is often the case in the intermediate and harder collections. It's the solver who learns. *** A more general moral of the story: resisting moves in tsumego are not to be emulated (unless sometimes for practical purposes, when there are no other winning chances in a game but to try to play bad moves in order to possibly induce even worse moves), but just to test the learner.