Λέγει ὁ ἰάμβλιχος ὅτι ἄνω τὸ συνδέσμῳ εἷς ἐπὶ συμπλεκτικῶν εἶπεν, τοὺς μὴ σημαίνοντας σχέσιν δύο πραγμάτων ἢ πολλῶν, ὡς τὸ Σωκράτης βαδίζει καὶ Πλάτων διαλέγεται, ἐνταῦθα δὲ συνδέσμῳ
εἷς εἶπεν αἰνιττόμενος τὰς ὑποθετικὰς προτάσεις, οἷον εἰ ὁ ἧλιος ὑπὲρ γῆν, ἡμέρα ἐστίν. οὐκ ἔστιν δὲ τοῦτο ἀληθές. οὐδὲ γὰρ ἔχει δεἴξαι ὅτι ἐπὶ τῆς ἐννοίας τάυτης τέθεικεν ὁ φιλόσοφος τὸ ἢ σθνδέσμῳ εἷς. ἀλλ’ ὥσπερ εἶπον, οὐδὲν ἀδύνατον ἓν τῶν σκελῶν τῆς διαρέσεως ἐν τῷ ἑτέρῳ θεωρεῖσθαι. αὐτὸς γὰρ παρακατιὼν λέγει εὐθὺς ὅτι ἁπλῆ ἀπόφανσις ἐστιν ἡ ἓν καθ’ ἑνὸς κατηγοροῦσα, σύνθετος δὲ ἡ ἐκ τοὐτων συγκειμένη. ὡσαύτως δὲ καὶ ἐπὶ τῶν ἀποφάσεων. ὥστε ἐν τοῖς τρισὶ σκέλεσιν ἐξ ἀνάγκης τὸ αὐτὸ εἶπεν κατὰ τὸν Ἀμμώνιον.
Iamblichus says that by ‘one by conjunction’ Aristotle refers above to copulative conjunctions that do not indicate a relation of two or more things, as in ‘Socrates walks and Plato talks.’ Here, on the other hand, by ‘one by conjunction’ he alludes to hypothetical/conditional sentences, such as ‘if the sun is above the earth, then it is daytime.’ This is not true. He cannot show that Aristotle uses ‘one by conjunction’ in this meaning, but, as I have stated, it is not impossible to contemplate one member of the division in another. A little further, he himself says that simple negation is the one with ‘one to one’ predication; composite negation is the one that is composed of simple negations. The same holds true for affirmation. According to Ammonius, he says by necessity the same with reference to the three members. The end of the lecture.
To get a preliminary handle on τὸ συνδέσμῳ εἷς without getting into the hardcore metaphysical stuff it’s worth reading through the relevant section in Aristotle’s Poetics (1457ab), the one I tell my students they can skip.
Various typos. Your τὸ ἢ σθνδέσμῳ should presumably be just τὸ συνδέσμῳ, without ἢ.
And your translation at several vital points seems questionable at best. All this really needs proper philosophical grounding and contextualization to be intelligible.