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Weakly Unambiguous Morphisms Freydenberger, Dominik D. Nevisi, Hossein Reidenbach, Daniel Combinatorics on words Morphisms Ambiguity A nonerasing morphism sigma is said to be weakly unambiguous with respect to a word w if sigma is the only nonerasing morphism that can map w to sigma(w), i.e., there does not exist any other nonerasing morphism tau satisfying tau(w) = sigma(w). In the present paper, we wish to characterise those words with respect to which there exists such a morphism. This question is nontrivial if we consider so-called length-increasing morphisms, which map a word to an image that is strictly longer than the word. Our main result is a compact characterisation that holds for all morphisms with ternary or larger target alphabets. We also comprehensively describe those words that have a weakly unambiguous length-increasing morphism with a unary target alphabet, but we have to leave the problem open for binary alphabets, where we can merely give some non-characteristic conditions. Schloss Dagstuhl – Leibniz-Zentrum für Informatik Dominik D. Freydenberger and Hossein Nevisi and Daniel Reidenbach 2011 Is Part Of LIPIcs, Volume 9, 28th International Symposium on Theoretical Aspects of Computer Science (STACS 2011) InProceedings Text doc-type:ResearchArticle publishedVersion application/pdf doi:10.4230/LIPIcs.STACS.2011.213 urn:nbn:de:0030-drops-30123 https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2011.213 eng https://creativecommons.org/licenses/by-nc-nd/3.0/legalcode