system. Letters are graphemes that broadly correspond to phonemes, the smallest functional units of sound in speech. Similarly to how phonemes are combined to form spoken words, letters may be combined to form written words. A single phoneme may also be represented by multiple letters in sequence, collectively called a multigraph. Multigraphs include digraphs of two letters (e.g. English ch, sh, th), and trigraphs of three letters (e.g. English tch).

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