How use common function and common politics?

[DmitryiVasiliev]

Hi!
I define policies for my projects and I have any questions:

1. How I can write a common function in rego file and use it in other policies, except import?
2. How I can define default policy if package does not exist yet. Example if I send request to path: /api/v1/data/service1 and policy with package service1 - not created, then I retrieve status 200 and empty body., but I want retrieve response from default policy
3. I see https://www.styra.com/blog/dynamic-policy-composition-for-opa/, but if I implement more difficult logic, policy always return false, target policy don't perform