وَفِي «لَيْسَ» خِلَافٌ.
Translation: Grammarians disagree about whether the khabar may be placed before the verb laysa.
The book registers a scholarly disagreement but does not present the full arguments. Learn the uncontroversial order «لَيْسَ زَيْدٌ قَائِمًا» before studying the disputed fronting.