digraph graph_name {
  graph [
    charset = "UTF-8";
    label = "証明木",
    labelloc = "t",
    labeljust = "c",
    bgcolor = "#343434",
    fontcolor = white,
    fontsize = 18,
    style = "filled",
    rankdir = TB,
    margin = 0.2,
    splines = spline,
    ranksep = 1.0,
    nodesep = 0.9
  ];

  node [
    colorscheme = "rdylgn11"
    style = "solid,filled",
    fontsize = 16,
    fontcolor = 6,
    fontname = "Migu 1M",
    color = 7,
    fillcolor = 11,
    fixedsize = true,
    height = 0.6,
    width = 3,
  ];

  edge [
    style = solid,
    fontsize = 14,
    fontcolor = white,
    fontname = "Migu 1M",
    color = white,
    labelfloat = true,
    labeldistance = 2.5,
    labelangle = 70
  ];

  // node define
  alpha [label = "ρ |- (x * z) - (y + z) => 3\n(OpR)",shape = box];
  beta [label = "ρ |- (x * z) => 8\n(OpR)",shape = box];
  gamma [label = "ρ |- (y + z) => 5\n(OpR)",shape = box];
  delta [label = "ρ |- x => 4 \n(VarR)",shape = box];
  epsilon [label = "ρ |- z => 2 \n(VarR)",shape = box];
  zeta [label = "ρ |- y => 3 \n(VarR)",shape = box];
  eta [label = "ρ |- z => 2 \n(VarR)",shape = box];


  // edge define
  alpha -> beta [arrowhead = normal];
  alpha -> gamma [arrowhead = normal];
  beta -> delta [arrowhead = normal];
  beta -> epsilon [arrowhead = normal];
  gamma -> zeta  [arrowhead = normal];
  gamma -> eta  [arrowhead = normal];
}