digraph {

  K6 -> K2
  K6 -> BH1
  K2 -> K1
  K2 -> K4

  K1 -> BH2
  K1 -> BH2

  K4 -> BH3
  K4 -> BH3

  K1 [label="K1 (distantNephew)",color="darkgray",fontcolor="darkgray"]
  K2 [label="K2 (sibling)",color="darkgray",fontcolor="darkgray"]
  K4 [label="K4 (closeNephew)",color="darkgray",fontcolor="darkgray"]
  K6 [label="K6 (parent)",color="darkgray",fontcolor="darkgray"]

  BH1 [shape="box",label="black height i + 1",style="dotted",fontname="Italic"]
  BH2 [shape="box",label="black height i + 2 - \nnumber of black nodes\nin { K1, K2 }",style="dotted",fontname="Italic"]
  BH3 [shape="box",label="black height i + 2 - \nnumber of black nodes\nin { K2, K4 }",style="dotted",fontname="Italic"]

}