I have some doubts how to turn a Partizipialattribut into a Relativsatz. Is there any rule? I know that I should use werden when the action is still in process and sein when the action is not in progress anymore, but it’s still unclear.
For example:
ein schriftlich vereinbarter Liefertermin → ein Liefertermin, der schriftlich vereinbart ist/wird(?)
My questions:
- Should I use werden or sein?
- Can you tell me why?
- Does it depend on the context?