To solve this problem, the following strategy is adopted: we appeal to the dictionary Delac in Unitex for labelling adjective multiword expressions, adverbial multi-word expressions, verbal multi-word expression and prepositional multi-word expressions ; these expressions are then replaced by the corresponding morphosyntactic label (like <ADV>, <ADJ>, <V> and <PREP>).
the multiword expression une fois acheté becomes <ADV> acheté after the preprocessing.