US-P17.011ab ।US-P17.011cd ॥
In plain words
This entire triad is therefore unreal, fabricated mutually through imagination. It is like a written letter, or a sound heard and then mentally projected outward.
Close to the Sanskrit
This triad is therefore unreal, constructed mutually by imagination; just as a letter is made, or as a sound heard from elsewhere is projected externally by the intellect.