Basically, a first- or second-person pronoun cannot be both subject and object. You cannot say jIH SoH je relegh jIH SoH je you and I see you and me.
My example was in error. A correction: you cannot say tlhIH relegh jIH SoH je You and I see you (plural) because you've got a second person in both subject and object positions. It doesn't have to be the same pronoun, just the same person of pronoun.
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