for (y = 1; y <= Bottom; y++) {
  if ([1,y] == "1" && [2,y] == "1") {
    [3,y] = "a";
  } else if ([1,y] == "2" && [2,y] == "1") {
    [3,y] = "b";
  } else if ([1,y] == "1" && [2,y] == "2") {
    [3,y] = "c";
  } else if ([1,y] == "2" && [2,y] == "2") {
    [3,y] = "d";
  }
}