#./interaufg864_en.tex#How many possibilities do exist to arrange the digits
in a 4x4 grid if

**a)**
- each digit appears 4 times, e.g.

1 |
1 |
1 |
1 |

2 |
2 |
3 |
3 |

4 |
2 |
2 |
3 |

4 |
4 |
4 |
3 |

**b)**
- in addition, all digits appear in each row, e.g.

1 |
2 |
3 |
4 |

1 |
3 |
4 |
2 |

3 |
2 |
4 |
1 |

3 |
4 |
2 |
1 |

**c)**
- moreover, no digit appears more than once in each column, e.g.

1 |
2 |
3 |
4 |

2 |
1 |
4 |
3 |

3 |
4 |
1 |
2 |

4 |
3 |
2 |
1 |

Fill in a grid where in addition to the constraints of a) - c) no identical digits are placed along the main diagonals.

**Answer:**

[solution to the problem of the previous week]