digraph {
  nd_0001 [
    shape=none
    
  label="A"
  ];

  nd_0002 [
    shape=none
    
  label="B"
  ];

  nd_0003 [
    shape=none
    
  label="C"
  ];

  nd_0004 [
    shape=none
    
  label="D"
  ];

nd_0001 -> nd_0002 [dir=both arrowhead=none arrowtail=odot];
nd_0002 -> nd_0003 [dir=both arrowhead=crow arrowtail=diamond];
nd_0003 -> nd_0004 [dir=both arrowhead=invempty arrowtail=tee];
}