Originally only the dual and plural showed the weak forms, which are retained in the second aorists of τίθημι, δίδωμι, and ἵ_ημι: ἔθεμεν, ἔδομεν, εἷμεν (ἐ-έμεν), and in Hom. βάτην (also βήτην) from ἔβην
a. For the singular of τίθημι, δίδωμι, ἵ_ημι, see cross755; for the imperatives, 759; for the infinitives, 760.
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].