Reference for Sanhedrin 212:15

אמר רב משרשיא דואג ואחיתופל לא [הוו] סברי שמעתא מתקיף לה מר זוטרא מאן דכתיב ביה איה סופר איה שוקל איה סופר את המגדלים ואת אמרת לא הוו סברי שמעתא אלא דלא הוה סלקא להו שמעתא אליבא דהלכתא דכתיב (תהלים כה, יד) סוד ה' ליראיו

R. Ammi said: Doeg and Ahitophel propounded four hundred problems with respect to a tower flying in the air, and not one was solved. Raba observed: Is there any greatness in propounding problems? In the years of Rab Judah the whole study was confined to Nezikin,<span class="x" onmousemove="('comment',' 'Damages', the fourth Order ([H]) of the Talmud. When Rab Judah was head of the academy of Pumbeditha, only the fourth Order was studied, but not the other Orders. This would appear to be the meaning of the passage. But Weiss, Dor III, 196ff, having regard to the abundance of contributions in Rab's name by Rab Judah on the other orders, explains the passage to mean; 'only as far as Nezikin.' i.e., the first four Orders. These being of practical utility, were intensively studied, and new laws stated. But as for the last two Orders dealing with sacrifices and ritual purity, though taught in the academy, no effort was made to formulate new laws, since the subjects were of no practical interest to Babylon, and Rab Judah contented himself with teaching only what had been transmitted to him. ');">²⁶</span> whilst we study a great deal even of 'Ukzin;<span class="x" onmousemove="('comment',' Name of a treatise of the Mishnah and the Tosefta, belonging to the sixth Order; lec. var. 'we study intensively the six Orders.' ');">²⁷</span>

Jastrow