What is the basic difference between illā alladhīna and law taʿlamūn?

Supplementary Practice 19: Comparative Rhetorical Analysis of Sūrat al-ʿAṣr and al-Takāthur

• Illā marks exception; law marks a condition with an unexpressed apodosis
• They are two pronunciations of the same negator
• Illā is always interrogative and law circumstantial wāw
• Both necessarily omit the subject