21. The authoring system of claim 19 , further comprising a lexicon, the comparator being configured to reject a sentence which includes a word which is not in the lexicon.
19. An authoring system comprising: a syntactic analyzer which is configured for analyzing a source sentence of a natural language input text and generating a syntactic representation of the source sentence; a text generator configured for generating a target sentence in the natural language of the source sentence, based on the syntactic representation of the source sentence; and a comparator configured for comparing the source sentence with the target sentence to determine whether there is a match and outputting a decision based on the comparison.