Rule reminder

Common errors with 'si impersonale': (1) Using plural verb with 'si' + transitive verb with plural object — the verb stays 3rd person singular only when there is no direct object; with a direct object, the participle agrees but the auxiliary is always 'essere'. (2) Adding reflexive 'si' when 'si impersonale' is already present (use 'ci si' for reflexive + impersonal). (3) Wrong tense in compound forms. (4) Using 'si' with a verb that already has a different subject. (5) Double 'si' error (si si → ci si).