In North & Hillard, Ex. 20, Q. 2, the student is invited to translate this sentence into Latin:
Those who wish to command ought to learn to obey.
I gave this translation: qui imperare volunt discere parere debent.
The answer book says this is correct except that the word ei should be included.
I know that imperare and parere take the dative case; but I thought that, here, both verbs are intransitive? Does the answer given mean to command or to obey "him"?
Is the inclusion of ei mandatory; would the sentence be correct without it?