TherapieGo: [current position] + B18A16C18B19C19E19A19 Look, it's work if outside is thick.
posetcay: Oh you meant that sequence, I thought you were talking about the seki shape. That sequence is the inferior way of making thousand year ko compared to starting directly with B2, so I don't feel like adding it. No need to make A3-A4 exchange if it doesn't change the state of the group.
TherapieGo: [current position] If A16 is sente then when we start with B18, we can play A16 sente and live with C18. In this case the problem is broken. Maybe we need to add a stone in B14 and there is 2 solution : B18 and A17.
posetcay: A3 doesn't work regardless of outside stone, fixed the refutation. I don't think there is a need to add an extra stone, D4 wall is so thick that A4 won't be sente. For example, B5-B7 and opponent can't escape. Or B5-B6-B7-C5-A6 is ko, but this is terrible for the opponent.
Oh you meant that sequence, I thought you were talking about the seki shape. That sequence is the inferior way of making thousand year ko compared to starting directly with B2, so I don't feel like adding it. No need to make A3-A4 exchange if it doesn't change the state of the group.