strict digraph sbox0i {
  x0 [shape=box, label="\N"];
  x1 [shape=box, label="\N"];
  x2 [shape=box, label="\N"];
  x3 [shape=box, label="\N"];

  t15 [label="\N\ny0\n1"];
  t02 [label="\N\ny2\n2"];
  t01 [label="\N\ny1\n3"];
  t05 [label="\N\ny2\n4"];
  t04 [label="\N\ny1\n5"];
  t03 [label="\N\nx2\n6"];
  t08 [label="\N\nx1\n7"];
  t06 [label="\N\ny1\n8"];
  t09 [label="\N\nx1\n9"];
  y1  [label="\N\n10", shape=box];
  t12 [label="\N\nx0\n11"];
  t13 [label="\N\nx0\n12"];
  t17 [label="\N\nx1\n13"];
  y2  [label="\N\n14", shape=box];
  t10 [label="\N\nx3\n15"];
  t14 [label="\N\nx3\n16"];
  y3  [label="\N\n17", shape=box];
  t18 [label="\N\nx1\n18"];
  y0  [label="\N\n19", shape=box];
  
  x2  -> t01; x3  -> t01;  // t01 = x2  ^ x3;
  x0  -> t02; x1  -> t02;  // t02 = x0  | x1;
  x1  -> t03; x2  -> t03;  // t03 = x1  | x2;
  x2  -> t04; t01 -> t04;  // t04 = x2  & t01;
  t01 -> t05; t02 -> t05;  // t05 = t02 ^ t01;
  x0  -> t06; t04 -> t06;  // t06 = x0  | t04;
  t05 -> y2;               // y2  =     ~ t05;
  x1  -> t08; x3  -> t08;  // t08 = x1  ^ x3;
  t03 -> t09; t08 -> t09;  // t09 = t03 & t08;
  x3  -> t10; y2  -> t10;  // t10 = x3  | y2;
  t06 -> y1;  t09 -> y1;   // y1  = t09 ^ t06;
  x0  -> t12; t05 -> t12;  // t12 = x0  | t05;
  y1  -> t13; t12 -> t13;  // t13 = y1  ^ t12;
  t03 -> t14; t10 -> t14;  // t14 = t03 ^ t10;
  x0  -> t15; x2  -> t15;  // t15 = x0  ^ x2;
  t13 -> y3;  t14 -> y3;   // y3  = t14 ^ t13;
  t05 -> t17; t13 -> t17;  // t17 = t05 & t13;
  t14 -> t18; t17 -> t18;  // t18 = t14 | t17;
  t15 -> y0;  t18 -> y0;   // y0  = t15 ^ t18;
}