jhubert: There is a Ko+ indication for T5 which is not good in one sequence: White connect the ko on S3 and black must defend on Q2 which let white make a second eye on S1. T5 is not a ko threat in this sequence.
posetcay: The file I created got swapped with something else because of the duplicate tsumego feature, perhaps the uploader of this version can take a look.
Ok.