The book lists ثُلَاث, مَثْلَث, أُخَر, and جُمَع for ʿadl + adjectival status.
ثُلَاث and مَثْلَث are distributive expressions meaning “three at a time / in threes.” أُخَر means “other” (feminine plural).
The original passage lists these forms; subsequent worked sentences are instructional elaborations, not further quotations from the book.