What does “ʿalā aḥad al-qawlayn” indicate for niʿma?

Iṭnāb: Clarification after Ambiguity, Tawshīʿ, Repetition and Īghāl

• More than one grammatical analysis exists
• Both views necessarily classify it as concision
• The construction admits no grammatical difference
• Only object-ellipsis is meant