وَفِي امْتِنَاعِ مُجَامَعَةِ «لَا» الْعَاطِفَةِ لِمَا سَبَقَ
It also shares the incompatibility of appending the coordinating lā to the restrictive construction described earlier.
مَا زَيْدٌ غَيْرُ شَاعِرٍ لَا كَاتِبٍ
“Zayd is none but a poet, not a writer” is not admitted in this precise grammatical arrangement.
Ghayr has already established the relevant exclusion. Adding a further coordinating lā in the same restrictive pattern creates a conflicting or redundant structure.
This is a rule about combining two specified constructions, not a universal prohibition on using coordinating lā elsewhere.