T. Gilmartin, (Professor of History, Maynooth, 1890), writes in Church History, Vol. 1, Ch XVII: The Arians sought the approval of an Ecumenical Council. They sought to hold two councils. Constantius, summoned the bishops of the East to meet at Seleucia in Isauria, and those of the West to Rimini in Italy. A preliminary conference was held by the Arians at Sirmium, to agree a formula of faith. A "Homoeon" creed was adopted, declaring The Son to be "like the Father". The two met in autumn of 359. At Seleucia, one hundred and fifty bishops, of which one hundred and five were semi-Arian. The semi-Arians refused to accept anything less than the "Homoiousion", (see: Homoiousian), formulary of faith. The Imperial Prefect was obliged to disband, without agreeing on any creed. Acacius, the leader of the "Homoean" party went to Constantinople, where the Sirmian formulary of faith was approved by the "Home Synod", (consisted of those bishops who happened to be present at the Court for the time), and a decree of deposition issued against the leaders of the semi-Arians. At Rimini were over four hundred of which eighty were Arian, the rest were orthodox. The orthodox fathers refused to accept any creed but the Nicene, while the others were equally in favour of the Sirmian. Each party sent a deputation to the Emperor to say there was no probability to agreement, and asked for the bishops to return to their dioceses. For the purpose of wearing-down the orthodox bishops; (Sulpitius Severius says), Constantius delayed his answer for several months, and finally prevailed on them to accept the Sirmian creed. It was after this Council that Jerome said: " ...the whole world groaned in astonishment to find itself Arian."

Answer this question, if possible (if impossible, reply "unanswerable"):  What was the belief that was disproved at this council?
unanswerable