In chess, if you say checkmate and your opponent isn't checkmated

Check, Checkmate, & Stalemate Differences Explained (with GIFs)

Check, Checkmate, & Stalemate Differences Explained (with GIFs)

Data center commissioning without the 5D chess - DCD

Check, Checkmate, & Stalemate Differences Explained (with GIFs)

8 Special Rules in Chess You Need To Know - The School Of Rook

It's the Implications We Fear — What Jay Thinks

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Lesson 3 – How to checkmate your opponent's king –

The Complete Checkmate Patterns List [with examples]

In chess, if my opponent says 'checkmate', does that end his turn, or is he allowed to continue to still hold on to his piece? - Quora

According to the rules of chess, what happens when a player achieves checkmate but doesn't call it out? - Quora

Chess Terminology - Remote Chess Academy