>>> old_IS:= {[i,j]: 1 <= i <= 8 & 1 <= j <= 4};
>>> T1:={[i,j] -> [j-i+8,i,0]};
>>> T2:={[i,j] -> [i+j-1,i,1]};
>>> n1:= T1 \ old_IS;
>>> n1;
{[i,j] -> [j-i+8,i,0] : 1 <= i <= 8 && 1 <= j <= 4}
>>> n2:= T2 \ old_IS;
>>> n2;
{[i,j] -> [i+j-1,i,1] : 1 <= i <= 8 && 1 <= j <= 4}
>>> codegen T1:old_IS,T2:old_IS;
for(t1 = 1; t1 <= 11; t1++) {
  for(t2 = max(t1-3,1); t2 <= min(t1,-t1+8); t2++) {
    s2(t2,t1-t2+1);
  }
  for(t2 = max(-t1+9,1); t2 <= min(-t1+12,t1-4); t2++) {
    s1(t2,t1+t2-8);
  }
  for(t2 = max(-t1+9,t1-3); t2 <= min(-t1+12,t1); t2++) {
    s1(t2,t1+t2-8);
    s2(t2,t1-t2+1);
  }
  for(t2 = max(-t1+9,t1+1); t2 <= min(-t1+12,8); t2++) {
    s1(t2,t1+t2-8);
  }
  for(t2 = max(t1-3,-t1+13); t2 <= min(t1,8); t2++) {
    s2(t2,t1-t2+1);
  }
}

>>> codegen 2 T1:old_IS,T2:old_IS;
for(t1 = 1; t1 <= 3; t1++) {
  for(t2 = 1; t2 <= t1; t2++) {
    s2(t2,t1-t2+1);
  }
  for(t2 = -t1+9; t2 <= 8; t2++) {
    s1(t2,t1+t2-8);
  }
}
for(t2 = 1; t2 <= 4; t2++) {
  s2(t2,-t2+5);
}
for(t2 = 5; t2 <= 8; t2++) {
  s1(t2,t2-4);
}
for(t2 = 2; t2 <= 3; t2++) {
  s2(t2,-t2+6);
}
for(t2 = 4; t2 <= 5; t2++) {
  s1(t2,t2-3);
  s2(t2,-t2+6);
}
for(t2 = 6; t2 <= 7; t2++) {
  s1(t2,t2-3);
}
for(t2 = 3; t2 <= 6; t2++) {
  s1(t2,t2-2);
  s2(t2,-t2+7);
}
for(t2 = 2; t2 <= 3; t2++) {
  s1(t2,t2-1);
}
for(t2 = 4; t2 <= 5; t2++) {
  s1(t2,t2-1);
  s2(t2,-t2+8);
}
for(t2 = 6; t2 <= 7; t2++) {
  s2(t2,-t2+8);
}
for(t2 = 1; t2 <= 4; t2++) {
  s1(t2,t2);
}
for(t2 = 5; t2 <= 8; t2++) {
  s2(t2,-t2+9);
}
for(t1 = 9; t1 <= 11; t1++) {
  for(t2 = 1; t2 <= -t1+12; t2++) {
    s1(t2,t1+t2-8);
  }
  for(t2 = t1-3; t2 <= 8; t2++) {
    s2(t2,t1-t2+1);
  }
}