Вот такая задача: расставить на шахматной доске минимальное количество ладей так, чтобы каждое поле было атаковано не меньше, чем 2-мя ладьями. Ладья может атаковать через другую ладью и не атакует поле на котором стоит.

Ответ: Двенадцать как минимум.

 1 2 3 4 5 6 7 8
 ___ ___ ___ ___ ___ ___ ___ ___
h | | | | | Л | Л | Л | |
 --- --- --- --- --- --- --- ---
g | Л | | | | | | | |
 --- --- --- --- --- --- --- ---
f | Л | | | | | | | |
 --- --- --- --- --- --- --- ---
e | Л | | | | | | | Л |
 --- --- --- --- --- --- --- ---
d | | | | | | | | Л |
 --- --- --- --- --- --- --- ---
c | | | | | | | | Л |
 --- --- --- --- --- --- --- ---
b | | | | | | | | Л |
 --- --- --- --- --- --- --- ---
a | | Л | Л | Л | | | | |
 --- --- --- --- --- --- --- ---