In “Inna Zaydan la-qāʾimun,” both inna and the lām strengthen the assertion. Their grammatical roles must still be distinguished: inna makes its noun accusative; the predicate remains nominative, while the lām adds affirmation before it.
The rhetorical task is not merely to count two markers. It is to explain how the speaker strengthens the assertion in response to doubt or denial. Emphasis does not invariably prove actual doubt: a speaker may rhetorically treat a listener as a denier.