Use four questions.
1. Is the particle أَنْ?
2. Which imperfect verb follows it?
3. Has that verb taken the correct Mudari Takhfif ending?
4. What noun-like meaning and sentence role does the complete expression carry?
Common errors:
● calling أَنْ alone Masdar Muawwal;
● forgetting to include the verb;
● keeping the inflectional nūn in a second-group form;
● assigning a sentence role without reading the full sentence.