What does it mean? > then you can check synthetic relations that refer to each permission individually I guess synthentic relation you meant something like this

definition folder {
  relation organization_viewer: organization#member
  relation public_viewer: user:*
  permission organization_viewer: organization_viewer
  permission public_viewer: public_viewer
}

But I still don't fully understand, how I can evaluate the permission for different subjects?

zed permission check folder:1 organization_viewer user:public_user # it's a public user and this request will return false, but in reality this relation exists despite organization_access: 'viewer' set in the database