The Supreme Court has held that "abstract ideas" can't be patented, but then has deliberately refrained from defining what an "abstract idea" is!
In the latest Alice decision, they write: "In any event, we need not labor to delimit the precisecontours of the “abstract ideas” category in this case. It is enough to recognize that there is no meaningful distinction between the concept of risk hedging in Bilski and the concept of intermediated settlement at issue here. Both are squarely within the realm of “abstract ideas” as we have used that term."
So you can't have "X", where "X" is undefined.