public boolean removePermission(WsecPermission permission) {
permission.getReceivingGroups().remove(this);
return permissions.remove(permission);
}
public boolean addPermission(WsecPermission permission) throws PermissionCollisionException {
PermissionExclusion.checkIfConflicts(this, permission);
permission.getReceivingGroups().add(this);
return permissions.add(permission);
}