(* ========================================================================= *)
(* Maximum number of references *)
def M_r () : natural = 2 end_def

(*========================================================================== *)
(* Basic predicates over actions *)

(* Parameterized predicates *)
macro isRequest (ref)      = EVAL_A (REQUEST !ref ...)       end_macro
macro isCancel (ref)       = EVAL_A (CANCEL !ref)            end_macro
macro isInvoice (ref)      = EVAL_A (INVOICE !ref)           end_macro

(*========================================================================== *)