>>> R1:={[i,j]: 2 <= i,j <= 9};
>>> R2:={[i,j]: 5 <= i <= 9 & 1 <= j <= 9};
>>> codegen R1,R2;
for(t1 = 2; t1 <= 9; t1++) {
  if (t1 >= 5) {
    s2(t1,1);
  }
  if (t1 <= 4) {
    for(t2 = 2; t2 <= 9; t2++) {
      s1(t1,t2);
    }
  }
  if (t1 >= 5) {
    for(t2 = 2; t2 <= 9; t2++) {
      s1(t1,t2);
      s2(t1,t2);
    }
  }
}

>>> codegen 2 R1,R2;
for(t1 = 2; t1 <= 4; t1++) {
  for(t2 = 2; t2 <= 9; t2++) {
    s1(t1,t2);
  }
}
for(t1 = 5; t1 <= 9; t1++) {
  s2(t1,1);
  for(t2 = 2; t2 <= 9; t2++) {
    s1(t1,t2);
    s2(t1,t2);
  }
}