 
class Folder implements Namespace {
	related: {
	  parents: File[]
	  viewers: SubjectSet<Group, "members">[]
	}

	permits = {
	  view: (ctx: Context): boolean => this.related.viewers.includes(ctx.subject),
	}
}

class File implements Namespace {
	related: {
	  parents: (File | Folder)[]
	  viewers: (User | SubjectSet<Group, "members">)[]
	  owners: (User | SubjectSet<Group, "members">)[]
	  siblings: File[]
	}

	// Some comment
	permits = {
	  view: (ctx: Context): boolean =>
	    (
		this.related.parents.traverse/* ||
		this.related.owners.) =>
		this.related.siblings.traverse(s => s.permits.edit(ctx)),
	}
}
