A B C D E F G H I J K L M N O
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  1 └┴┴┴┴┴┴┴┴┴┴┴┴┴┘ 

[ 1]● ==> H8   [ 2]○ ==> H9   [ 3]● ==> J10  [ 4]○ ==> I9   [ 5]● ==> J8
[ 6]○ ==> I8   [ 7]● ==> I7   [ 8]○ ==> G9   [ 9]● ==> J9   [10]○ ==> J7
[11]● ==> G10  [12]○ ==> I11  [13]● ==> I10  [14]○ ==> H10  [15]● ==> J12
[16]○ ==> J11  [17]● ==> H11  [18]○ ==> F9   [19]● ==> E9   [20]○ ==> K8
[21]● ==> I6   [22]○ ==> H6   [23]● ==> E7