>>> T1:={[i,j]->[j,i,0]};
>>> T2:={[i,j]->[j,i,1]};
>>> R2:={[i,j]: 1 <= i,j <= 9 && exists (alpha: j = 4alpha)};
>>> R3:={[i,j]: 1 <= i,j <= 9 && exists (alpha: j = 2alpha)};
>>> codegen T1:R2,T2:R3;
for(t1 = 2; t1 <= 8; t1 += 2) {
  if (intMod(t1,4) == 0) {
    for(t2 = 1; t2 <= 9; t2++) {
      s1(t2,t1);
      s2(t2,t1);
    }
  }
  if (intMod(t1-2,4) == 0) {
    for(t2 = 1; t2 <= 9; t2++) {
      s2(t2,t1);
    }
  }
}

>>> codegen 2 T1:R2,T2:R3;
for(t1 = 2; t1 <= 8; t1 += 2) {
  if (intMod(t1,4) == 0) {
    for(t2 = 1; t2 <= 9; t2++) {
      s1(t2,t1);
      s2(t2,t1);
    }
  }
  if (intMod(t1-2,4) == 0) {
    for(t2 = 1; t2 <= 9; t2++) {
      s2(t2,t1);
    }
  }
}