t0 = IO.inspect(Khf3.satrak_mx({2,3}, [{2,2}], [:N])) ===
  [[0,1,0],[0,0,0]]

t1 = IO.inspect(Khf3.satrak_mx({2,3}, [{2,2}], [:E])) ===
  [[0,0,0],[0,0,1]]

t2 = IO.inspect(Khf3.satrak_mx({2,3}, [{3,2}], [:N])) ===
  nil

t3 = IO.inspect(Khf3.satrak_mx({2,3}, [{2,2}], [:S])) ===
  nil

t4 = IO.inspect(Khf3.satrak_mx({2,3}, [{1,1},{2,2}], [:E,:N])) ===
  nil

t5 = IO.inspect(Khf3.satrak_mx({4,5}, [{2,4},{1,5},{3,2}], [:S,:W,:W])) ===
  [[0, 0, 0, 1, 0],
   [0, 0, 0, 0, 0],
   [1, 0, 0, 1, 0],
   [0, 0, 0, 0, 0]]

t6 = IO.inspect(Khf3.satrak_mx({6,6}, [{1,3},{1,5},{3,1},{4,6},{5,1},{5,4},{6,5}], [:S,:E,:N,:W,:E,:S,:E])) ===
  [[0, 0, 0, 0, 0, 1],
   [1, 0, 1, 0, 0, 0],
   [0, 0, 0, 0, 0, 0],
   [0, 0, 0, 0, 1, 0],
   [0, 1, 0, 0, 0, 0],
   [0, 0, 0, 1, 0, 1]]

IO.puts "#{t0}, #{t1}, #{t2}, #{t3}, #{t4}, #{t5}, #{t6}"