This is a stereogenic carbon, and this is a stereogenic carbon. Likewise, 1234. So these are all stereogenic carbons. Now, these are epimers, because they only differ in their stereo chemistry at a single one of these chiral carbon atoms. And let's see which one that is. So, if we begin at the first carbon, the first chiral carbon, notice that the hydroxyl group points to the right and the hydroxyl group here points to the right as well.