>>> IS:={[i,j]: 1 <= i,j <= 9};
>>> T1:={[i,j]->[4j,i,0]};
>>> T2:={[i,j]->[j,i,1]};
>>> codegen T1:IS,T2:IS;
for(t1 = 1; t1 <= 36; t1++) {
  if (intMod(t1,4) == 0 && t1 <= 8) {
    for(t2 = 1; t2 <= 9; t2++) {
      s1(t2,intDiv(t1,4));
      s2(t2,t1);
    }
  }
  if (intMod(t1,4) == 0 && t1 >= 12) {
    for(t2 = 1; t2 <= 9; t2++) {
      s1(t2,intDiv(t1,4));
    }
  }
  if (t1-3 <= 4*intDiv(t1-1,4) && t1 <= 9) {
    for(t2 = 1; t2 <= 9; t2++) {
      s2(t2,t1);
    }
  }
}

>>> codegen 2 T1:IS,T2:IS;
for(t1 = 1; t1 <= 8; t1++) {
  if (intMod(t1,4) == 0) {
    for(t2 = 1; t2 <= 9; t2++) {
      s1(t2,intDiv(t1,4));
      s2(t2,t1);
    }
  }
  if (t1-3 <= 4*intDiv(t1-1,4)) {
    for(t2 = 1; t2 <= 9; t2++) {
      s2(t2,t1);
    }
  }
}
for(t2 = 1; t2 <= 9; t2++) {
  s2(t2,9);
}
for(t1 = 12; t1 <= 36; t1 += 4) {
  for(t2 = 1; t2 <= 9; t2++) {
    s1(t2,intDiv(t1,4));
  }
}