#!r6rs
(library (rsc3 graphdef mrg)
(export Mrg make-mrg mrg? mrg-roots)
(import (rnrs))

(define-record-type mrg (fields roots))

(define (Mrg . roots)
  (if (null? roots)
      (error 'Mrg "empty mrg")
      (make-mrg roots)))

)