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mathcastles reference

Tic-tac-toe / Noughts and Crosses — rendered in blackletter Unicode

𝕺 (Mathematical Bold Fraktur O) and 𝖃 (Mathematical Bold Fraktur X) are the O and X of tic-tac-toe, rendered in ornate medieval type. 🞗 (crossed square) serves as the separator between the two players' pieces. Biome 76 appears to be a variant of this set, mixing in 城 (castle) — possibly a chess rook or Hypercastle allusion.