In French, the adverbial pronoun "y" is usually placed before a verb. In L'Impératif, it is not the case.
Position of the pronoun "y" in L'Impératif in French
Look at these sentences in L'Impératif:
aller (to go *somewhere*)
Note that in L'Impératif, the pronoun y is placed after the verb with a hyphen in between.
In the tu form, -ER verbs recover their original -s in front of y (for pronunciation reasons):
See also Using French adverbial pronoun "en" in affirmative commands in the imperative mood (L'Impératif) in French
and Conjugate regular verbs in the imperative mood in French (L'Impératif)
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