Leagues are listed here from lowest (entry-level) to highest difficulty:
Bronze
Silver
Gold
Sapphire
Ruby
Emerald
Amethyst
Pearl
Obsidian
Diamond
Mission accomplished!
Potential Discovery or Invention
Here is a chess position with multiply-twinned pieces during my match with Oscar.
Here is a chess position when Oscar (WHITE) called "Check", but he should have declared "Checkmate".
However, my geological engineer/exploration geologist daughter Évelyne pointed out that I (BLACK) could have done "en passant" to eat the WHITE pawn in this situation.
