Example scenario

Thread / Class	Permissions	Effective Thread Permission
Class 1	{ P1, P2 }	{ P1, P2 }
Class 2	{ P1, P3 }	{ P1 }
Class 3	{ P2 }	{ }
Class 4	{ P1, P5 }	{ }
checkPermission(P1)
fails
Pc1 3 Pc2 3 Pc3 3 Pc4 = { }