 1 0 0 0 0 0 4 0 0
 0 0 5 2 0 0 0 0 8
 0 0 0 0 7 0 0 0 0
 8 0 0 0 0 5 0 1 0
 0 0 0 0 0 0 0 0 0
 0 3 0 9 0 0 0 0 6
 0 0 0 0 4 0 0 0 0
 6 0 0 0 0 9 3 0 0 
 0 0 2 0 0 0 0 0 7

very hard
from ctc letter from dontsaymyid
in pattern overlay discussion
