Chess - block of stamps mint never hinged, Central Africa

This block of stamps on the subject of "chess" was published in Central Africa on June 25, 2012 and contains four stamps. The stamps of 900 F each show the chess players Magnus Carlsen, Anatoli Evgenjewitsch Karpow, Viswanathan Anand and Garri Kimowitsch Kasparow. The edge of the block is illustrated with various chess figures.
Chess is a board game for two people. One player plays with the white pieces, the other player with the black pieces. At the beginning of the game, both players have 16 pieces: a king, a queen, two bishops, two knights, two rooks and eight pawns. The aim of the game of chess is to checkmate the opponent.