-interpretation "relation invertion" 'invert a = (invert_os_relation _ a).
-interpretation "relation invertion" 'invert_symbol = (invert_os_relation _).
-interpretation "relation invertion" 'invert_appl a x = (invert_os_relation _ a x).
+interpretation "relation invertion" 'invert a = (invert_os_relation ? a).
+interpretation "relation invertion" 'invert_symbol = (invert_os_relation ?).
+interpretation "relation invertion" 'invert_appl a x = (invert_os_relation ? a x).