Why are you sure that Assad would agree on this?
Because the Kurds can cut ISIS off from the rest of the Turkish Border that they don’t already control.
Lots of news yesterday that the Kurds had made a significant advance under the cover of heavy Russian Airstrikes. (and with some new Russian toys of their own).
So much so that Obama’s “Moderate” Headchoppers are threatening to come to AQ’s aid, if the Kurds don’t withdraw.
“Why are you sure that Assad would agree on this?”
Because Putin tells him to.