The first of them is a classic readability formula by Kandel and Moles (1958), which is an adaptation of the Flesch (1948) formula for French: where Y is a readability score ranging from 100 (easiest) to 0 (harder); lp is the average number of words per sentence and lm is the average number of syllables per 100 words.
it seemed unlikely that the information collected by means of syntactic parsers, which are still committing a significant number of errors, at least for French, would belie these findings.