 The imperative uses the strong stem in all of the 1st person forms, as well as the 3rd person singular active.The 2nd person active may have no ending (class 5, class 8), "-dhi" (most of class 3,7, as well as class 1 ending in consonants), or "-hi" (class 9, class 3 in "ā", and class 1 in vowels; these classes usually ended in laryngeals in Proto-Indo-European)
The perfect system includes only the perfect.The stem is formed with reduplication; the reduplicated vowel is usually "a", but "u" or "i" for verbs containing them.