I searched a little about Harivarman, but I could not find much. It seems that he was seen as conterpart of both great schools and both refer him as one of the opposite "sect".
A Buddhist monk from central India, sometimes thought to be a member of the Bahuśrutīya subschool of the Mahāsaṃghikas, although his writings seem straightforwardly Sautrāntika. Reputedly a native of Kashmir he studied under the Sautrāntika master Kumāralāta before becoming dissatisfied with the conflicting views of the schools and desiring to reconcile their positions in a manner consonant with the original teachings of the Buddha. To this end he composed a treatise called the Tattvasiddhi Śāstra (also known as the Satyasiddhi Śāstra). His only surviving work, it is extant only in Chinese. It attained some popularity due to a mistaken belief that it taught orthodox Mahāyāna doctrines, such as emptiness (śūnyatā). In this work, which is divided in accordance with the Four Noble Truths, the author discusses a multitude of technical problems in Buddhist doctrine, and rejects those opinions which are not sanctioned by scripture. He follows the interpretation of no single school and states that he wishes to establish his own conclusions independently. He argues strongly for the recognition of the role played by the mind in the construction of reality through the medium of concepts and intellectual constructions (prajñapti). The present value of the treatise to scholars is as a compendium of proto-Mahāyāna teachings.
I also like to share a book of his work that I got from a monk: SATYASIDDHIŚĀSTRA
Just that! *smile* ...We Buddhists must find the courage to leave our temples and enter the temples of human experience, temples that are filled with suffering. If we listen to Buddha, Christ, or Gandhi, we can do nothing else. The refugee camps, the prisons, the ghettos, and the battlefields will become our temples. We have so much work to do. ... Peace is Possible! Step by Step. - Samtach Preah Maha Ghosananda "Step by Step" http://www.ghosananda.org/bio_book.html
BUT! it is important to become a real Buddhist first. Like Punna did: Punna Sutta Nate sante baram sokham _()_
Harivarman, who belonged to the Darvwantikas according to Lü (1982: 172) or to the Sautrantika-Darvwantikas according to Ven. Yinshun (1968: 574), but to the Bahunrutcyas according to Buswell and Jaini (1996: 94)
Just that! *smile* ...We Buddhists must find the courage to leave our temples and enter the temples of human experience, temples that are filled with suffering. If we listen to Buddha, Christ, or Gandhi, we can do nothing else. The refugee camps, the prisons, the ghettos, and the battlefields will become our temples. We have so much work to do. ... Peace is Possible! Step by Step. - Samtach Preah Maha Ghosananda "Step by Step" http://www.ghosananda.org/bio_book.html
BUT! it is important to become a real Buddhist first. Like Punna did: Punna Sutta Nate sante baram sokham _()_