strict digraph sbox6i {
  x0 [shape=box];
  x1 [shape=box];
  x2 [shape=box];
  x3 [shape=box];

  y0 [shape=box];
  y1 [shape=box];
  y2 [shape=box];
  y3 [shape=box];

  // Get to y1
  t01 [label="\N\ny2\n1"];
  t02 [label="\N\nx2\n2"];
  t06 [label="\N\ny0\n3"];
  t08 [label="\N\ny1\n4"];
  y1  [label="\N\n5"];
  // Get to t05
  t03 [label="\N\ny3\n6"];
  t05 [label="\N\ny3\n7"];
  // Get to t07
  t16 [label="\N\nx3\n8"];
  t04 [label="\N\nx2\n9"];
  t07 [label="\N\nx2\n10"];  
  // Get to y0
  t09 [label="\N\ny0\n11"];
  y0  [label="\N\n12"];
  // Get to y3
  t13 [label="\N\ny3\n13"];
  t15 [label="\N\ny3\n14"];
  t17 [label="\N\nx0\n15"];
  y3  [label="\N\n16"];
  // Get to y2
  t12 [label="\N\nx1\n17"];
  t14 [label="\N\ny2\n18"];
  y2  [label="\N\n19"];
    
  x0  -> t01; x2 -> t01;  // t01 = x0  ^ x2;
  x2  -> t02;             // t02 =     ~ x2;
  x1  -> t03; t01-> t03;  // t03 = x1  & t01;
  x1  -> t04; t02-> t04;  // t04 = x1  | t02;
  x3  -> t05; t03-> t05;  // t05 = x3  | t03;
  x1  -> t06; x3 -> t06;  // t06 = x1  ^ x3;
  x0  -> t07; t04-> t07;  // t07 = x0  & t04;
  x0  -> t08; t02-> t08;  // t08 = x0  | t02;
  t07 -> t09; t05-> t09;  // t09 = t07 ^ t05;
  t06 -> y1;  t08-> y1;   // y1  = t06 ^ t08;
  t09 -> y0;              // y0  =     ~ t09;
  x1  -> t12; y0 -> t12;  // t12 = x1  & y0;
  t01 -> t13; t05-> t13;  // t13 = t01 & t05;
  t01 -> t14; t12-> t14;  // t14 = t01 ^ t12;
  t07 -> t15; t13-> t15;  // t15 = t07 ^ t13;
  x3  -> t16; t02-> t16;  // t16 = x3  | t02;
  x0  -> t17; y1 -> t17;  // t17 = x0  ^ y1;
  t17 -> y3;  t15-> y3;   // y3  = t17 ^ t15;
  t16 -> y2;  t14-> y2;   // y2  = t16 ^ t14;
}