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Yasvamiśtra, Mohaniya, Haṇḍa-sthāna and Sevāt-saṁhanana - these four Prakṛtis are not bound. Because the binding of these four Prakṛtis occurs during the time of Mithyātva's arising. But at the time of Sāsvādana, Mithyātva does not arise. That is, Naraka-trika, Jāri-catuṣka, sthāvara-catuṣka, Haṇḍa-sthāna, Ātapa-nāma, Mevāt-saṁhanana, Napuṣaka-veda and Mithyātva-mohaniya - these sixteen Prakṛtis are bound due to Mithyātva. Out of these, Naraka-trika, Sūkṣma-trika, Vikala-trika, Eka-indriya-jāti, sthāvara-nāma and Ātapa-nāma - these twelve Prakṛtis are not bound by the Nārakīya Jīvas due to their different nature. Therefore, by taking them in Deva-dvīka etc., these twelve Prakṛtis are reduced at the time of general binding. And the remaining Napuṣaka-veda, Mithyātva-mohaniya, Haṇḍa-sthāna and Mevāt-saṁhanana - these Prakṛtis are bound due to Mithyātva, and Mithyātva does not arise in the Sāsvādana Guṇasthāna. Therefore, in the Sāsvādana Guṇasthāna, by reducing these four Prakṛtis from the 100 Prakṛtis that are bound by the Māraka Jīvas residing in the Mithyātva Guṇasthāna, the 66 Prakṛtis of the other Nārakīya Jīvas residing in the Sāsvādana Guṇasthāna are not eligible for binding.
The summary is that out of the 120 Prakṛtis that are eligible for binding, in the Naraka-gati, compared to the general binding, 101 Prakṛtis are bound because 16 Prakṛtis are not eligible for binding from the Ātāpa-nāmakarma up to the Sura-dvīka etc.
In the Naraka-gati, there are four Guṇasthānas from the first to the ninth. Therefore, out of the 101 Prakṛtis that are eligible for binding in the Naraka-gati, the binding of the Tīrthaṅkara Nāmakarma is due to Samyaktva, and since the Tīrthaṅkara Nāmakarma is not bound by the Nārakīya Jīvas residing in the Mithyātva Guṇasthāna, 100 Prakṛtis are bound, and the binding of the four Prakṛtis like Napuṣaka-veda etc. occurs when Mithyātva arises. And since Mithyātva does not arise in the Sāsvādana Guṇasthāna, by reducing the four Prakṛtis like Napuṣaka-veda etc. from the 100 Prakṛtis that are eligible for binding in the Mithyātva Guṇasthāna, 66 Prakṛtis are bound.