anchor.diff:      (values (not (zerop (mem-ref flag* :int))) request)))
   
   (defun mpi-wait (request)
  +  "Blocks until REQUEST has been completed."
     (declare (type mpi-request request))
     (with-foreign-objects ((status* '(:struct mpi-status))
                            (request* 'mpi-request))
  
positive.code: (defun mpi-iprobe (source &key
                              (tag +mpi-any-tag+)
                              (comm *standard-communicator*))
    "MPI-IPROBE checks whether a message with matching TAG and SOURCE has
  been sent on the communicator COMM. If so, it returns three values: The
  size of the incoming message in bytes, and the ID and TAG of the
  sender. Otherwise, it returns false."
    (declare (type int source tag)
             (type mpi-comm comm))
    (with-foreign-objects ((status '(:struct mpi-status))
  
negative.code:                                end
                                 (tag 0)
                                 (mode :basic))
    "A non-blocking variant of MPI-SEND. Returns a MPI-REQUEST that can be
  passed to MPI-TEST, MPI-WAIT and MPI-WAITALL.
  
  WARNING: The caller of MPI-ISEND is responsible that the given array is not
  relocated or garbage-collected until the send operation is complete. This can
  