For Dr. Mastronarde’s work, Unit 29, exercise 16, I have to give the 2nd singular intransitive aor. act. imperative of ἀποδύω. Fist, I set ἀπο aside and worry about that at the end. The chart on page 247 says the aorist active was is δῦθι; however, I did not know if the chart was for weak aorist or both weak and strong aorist?
δῦθι is intransitive and strong (second) aorist. Weak (first) aorists have a σ.
There is much to be said for the approach taken in the Cambridge Grammar of Classical Greek which talks about three types of aorist stem (sigmatic, thematic and root) etc.