at the first of the Mounce BBG 3rd edition pages(before the table of contents), He gives a quote from LXX
ΨΑΛΜΟΙ ΙΗ 8-10, 15
the interesting part for me is that, at the first-half of the second line (it appears to be verse 9)
It reads, τἁ δικαιώματα κυρίου εὐθεῖα, εὐφραίνοντα καρδἰαν·
it seems to me that εὐθεῖα is a female singular adjective and is predicating the neuter plural noun τἁ δικαιώματα. is it possible ...