https://kconrad.math.uconn.edu/blurbs/proofs/binomcoeffintegral.pdf
写作 ，定义为 的多项式展开式中， 项的系数，因此一定是非负整数。 (n > k)
定义：
理解：从 n 个里面选，k 个为一组，剩下为一组，内部排列
BNCF
- Definition:
- α → β is a trivial functional dependency (i.e., β ⊆ α).
- α is a superkey for schema R.
Decomposing schemas that are not in BCNF
- (α ∪ β)
- (R − (β − α))
- In the case of in dep above, α = dept name, β = {building, budget}, and in_dep is replaced by
- (α ∪ β) = (dept name, building,budget)
- (R − (β − α)) = (ID, name, dept name, salary)