I spent many dejected days trying to understand the following rule in this lesson. "the main difficulty here is that in French you cannot use a conjugated verb after la veille or le lendemain, unlike in English: the day after he left / the day before you were born.
Instead you will use de + noun, as such:'
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The imperative appeared out of the blue. (I am not using imperative here in the grammar sense by the way but as a prohibitory order) It also seemed contradictory, because the sentence, 'The day after, I was enrolling at university/ Le lendemain, j'allais m'inscrire à l'université. came right before it. ...a conjugated verb 'j allais' following lendemarin.
What seems to be the case is that 'le lendemain' or 'la veille' CANNOT be 'conjoined' with a descriptive clause or phrase for associated events WITHOUT punctuation. You identify the day using le lendemain or la veille but to add associated actions you must express them with a separate punctuated clause/phrase or use 'de + noun".
Examples:
the day after i was enrolling at university.../ le lendemain de mon inscription à l'université
the day after, I was enrolling at university...Le lendemain, je m'inscrivais à l'université.