Complex sentence: Nor is it to put a photon detector on the far side of the slit wall but near to one or both of the slits, but to put tubes pointed at each of the two slits near the detector wall.
Split into simpler sentences: Nor is it to put a photon detector on the far side of the slit wall but near to one or both of the slits. Instead the plan is to put tubes pointed at each of the two slits near the detector wall.