Much of the reporting on the Cala Homes litigation has focused on the question of the lawfulness of taking into account, in the context of a planning application or appeal, the Secretary of State's declared intention to revoke RS. We now know that this is an issue which goes to weight rather than materiality. However, that is only part of that particular picture. Where the question is one of soundness eg, of a core strategy, then there is no discretion - the core strategy must be in general conformity with RS (s 24, PCPA 2004) and the intention to revoke RS must not be taken into account (Cala). Of course some core strategies will rely on cross boundary support for deliverability - sometimes part of authority A's housing will need to lie within the area of authority B. So what happens where authority A's core strategy, compliant with RS, cannot deliver because neighbouring authority B, in reliance on the policy to revoke RS, decides to no longer provide that support? The answer is that the core strategy for authority A must be found unsound - it may be RS compliant, but no longer deliverable. This is what happened recently with the Stevenage Core Strategy and it demonstrates the critical importance of cross boundary cooperation. Does any reader have wisdom to impart on how best to manage these situations?