Parity

Rules

Place either of the letters E (even) or O (odd) into each cell. In cells pointed by black arrows, the placed letter must be the "sum" of letters placed in the cells the arrows grow from. In cells pointed by white arrows, the placed letter must be the "product" of letters placed in the cells the arrows grow from.

(Example from WPC 2015 IB)

History of the puzzle

Invented by Kazunori Saitoh (Japan). First appeared on WPC 2015/Round 10.

Appearances in the past WPCs

• WPC 2015/Round 10 by Kazunori Saitoh