PROCEDURE DepthLabel(
    coins: Random.T;
    READONLY e: ARRAY OF Edge;
    VAR uLab, vLab: ARRAY OF CARDINAL;
  ) =
  VAR uTop, vTop: CARDINAL := 0;
  BEGIN
    WITH
      NU = NUMBER(uLab),
      NV = NUMBER(vLab),
      NE = NUMBER(e),

      (* The neighbors of "u" are uAdj[uFirst[u]..uLast[u]] *)
      (* The corresponding entries in "e" are uEdge[uFirst[u]..uLast[u]] *)
      (* U vertices with unexplored edges are uStack[0..uTop-1] *)
      (* Ditto for V *)
      
      uFirst = NEW(REF ARRAY OF CARDINAL, NU+1)^,
      uLast = NEW(REF ARRAY OF CARDINAL, NU+1)^,
      uAdj = NEW(REF ARRAY OF CARDINAL, NE)^,
      uEdge = NEW(REF ARRAY OF CARDINAL, NE)^,
      uStack = NEW(REF ARRAY OF CARDINAL, NU)^,

      vFirst = NEW(REF ARRAY OF CARDINAL, NV+1)^,
      uLast = NEW(REF ARRAY OF CARDINAL, NV+1)^,
      vAdj = NEW(REF ARRAY OF CARDINAL, NE)^,
      VEdge = NEW(REF ARRAY OF CARDINAL, NE)^,
      vStack = NEW(REF ARRAY OF CARDINAL, NV)^
    DO
      CollectEdges(e, uFirst, uAdj, vFirst, vAdj);
      nEdges := NE;
      WHILE nEdges > 0 DO
        (* Pick a first edge: *)
        WITH
          ie = RC(coins, 0, nEdges)
        DO
          u := e[ie].u;
          v := e[ie].v;
          RemoveEdge(u, v);
          uStack[uTop] := u; INC(uTop);
          vStack[vTop] := v; INV(vTop);
          WHILE uTop > 0 OR vTop > 0 DO
            IF (vTop = 0) OR (uTop # 0 AND RB(coins)) THEN
              DEC(uTop); u := uStack[uTop];
              IF uFirst[u] <= uLast[u] THEN
                v := uAdj[RC(coins, uFirst[u], uLast[u])];
                
            ELSE
            END
          END
        END;
      END
    END
  END DepthLabel;
  
      IF ParseParams.KeywordPresent("-order") THEN
        ot := ParseParams.GetNext();
        IF Text.Equal(ot, "Random") THEN
          o.order := Order.Random
        ELSIF Text.Equal(ot, "Depth") THEN
          o.order := Order.Depth
        ELSIF Text.Equal(ot, "Breadth") THEN
          o.order := Order.Breadth
        ELSE
          Wr.PutText(stderr, "bad order: " * ot & "\n");
          RAISE Scan.BadFormat
        END;
      ELSE
        ot := "Random";
        o.order := Order.Random
      END;