Cognitive complexity theory (CCT) was an early technique to semi-formally assess interfaces . CCT had a simple state model of the computer interface and a production system as a cognitive model of the user, the two could be analysed to verify properties or dynamically 'played' together.
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Executing a production rule in CCT. From chaoter 2 a href"https://hcibook.com/e3/chaps/ch12">Cognitive Models in Human Computer Interacton, Dix, Finlay, Abwod, Beale (2004).