+let (+^) = Int64.add
+let (-^) = Int64.sub
+let ( *^ ) = Int64.mul
+let (/^) = Int64.div
+
+type ('a, 'b) either = Left of 'a | Right of 'b
+
+let verbose = ref false
+let set_verbose_flag () = verbose := true
+let verbose () = !verbose
+
+let write_flag = ref false
+let set_write_flag () = write_flag := true
+let write_flag () = !write_flag