caranthir: Yeah, you're right. Somehow I've overlooked the simplest way so far, the simplest way being that defender can force a ko. Updated. Sorry that this is starting to become a bit messy.
stone_juggler: caranthir, I believe after B18 A17 C18 D17 F19 B19 A18 E19 C19 G19 F17 defender could just go out H18 since there no attacker's stone outside. Attacker is also in loss of liberties inside, so defender could return later and capture inside stones when he would heve enough liberties outside. Or, at least, defender could make an eye outside and it will be a seki.
caranthir: Thanks. It seems that there should be some extra stone in the side to help attacker refute the running out situation. Modified the problem accordingly.
stone_juggler: In the main variation after w B18 A17 C18 D17 F19 black would play B19 instead of E19 and will live
caranthir: After defender B19, attacker should play A18. Now C19 and E19 are miai to kill. If E19, C19, G19, then F17 and defender is in loss of liberties to approach inside stones.
Yeah, you're right. Somehow I've overlooked the simplest way so far, the simplest way being that defender can force a ko. Updated. Sorry that this is starting to become a bit messy.