What is the rule or principle for identifying the implied "lām al-qasam" (oath particle), and is it called "lām at-tawkīd" (emphasis particle)?

The most important linguistic rule for the elided lam of oath is that it must be followed by the nun of emphasis (nūn al-tawkīd), examples of which include the Almighty's sayings: "You will surely find the most intense of people in animosity toward the believers to be the Jews" (لَتَجِدَنَّ أَشَدَّ النَّاسِ عَدَاوَةً لِّلَّذِينَ آمَنُواْ الْيَهُودَ) and "You will surely see the Hellfire" (لَتَرَوُنَّ الْجَحِيمَ). It can also be identified through meaning and context.

The lam of oath is most often confused with the lam of inception (lām al-ibtida') due to their shared characteristics of being open (fatḥah), their entitlement to appear at the beginning of a sentence, and their function of emphasis and verification. Both are open and precede sentences, emphasizing them. However, if a present tense verb is followed by the heavy or light nun, then it is a lam of oath, regardless of whether the oath was explicitly mentioned before it or not.