Herbert Weir Smyth, A Greek Grammar for Colleges

περὶ δ᾽ οὗ πρότερον . . . ἔθηκε νόμου διελθών (for τοῦ νόμου δ̀ν) dealing in detail with the law which he formerly passed D. 24.61, ἐπορεύετο σὺν ᾗ εἶχε δυνάμει (for σὺν τῇ δυνάμει ἣν) he advanced with what force he had X. H. 4.1.23. Even when the antecedent is omitted, the attraction takes place: πρὸς ᾧ εἶχε συνέλεγε . . . στράτευμα (for πρὸς τούτῳ τῷ στρατεύματι δ̀) he was collecting an army in addition to that which he had X. H. 4.1.41.

a. But a genitive or dative antecedent, when incorporated, is attracted into the case of a nominative relative. Thus, ἐν δικαστηρίοις καὶ ὅσοι ἄλλοι δημόσιοι σύλλογοι (sc. εἰσί) in courts and all the other public assemblies P. Phae. 261a (for τοσούτοις ἄλλοις συλλόγοις, ὅσοι δημόσιοί εἰσι).

b. When an antecedent in the genitive or dative is incorporated, the place of the antecedent is usually taken by a demonstrative pronoun in the genitive or dative. Thus, ““οὐδέ νυ τῶν περ μέμνηαι, ὅσα δὴ πάθομεν κακά” nor do you remember all the evils we suffered” Φ 441.