### Picture codes

Symeon Bozapalidis, Archontia Grammatikopoulou (2006)

RAIRO - Theoretical Informatics and Applications

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We introduce doubly-ranked (DR) monoids in order to study picture codes. We show that a DR-monoid is free iff it is pictorially stable. This allows us to associate with a set of pictures a picture code which is the basis of the least DR-monoid including . A weak version of the defect theorem for pictures is established. A characterization of picture codes through picture series is also given.