集合

Set

空集：empty set

属于：x is a number of R 或 x is in R

子集：A is a subset of B

真子集：A is a proper subset of B 或 A is properly included in B

交集：the intersection of A and B

并集：the union set of A and B

差集：the different set

α→β(α==>β)：α implies β 或 if β, then α.

α <==> β：α is equivalent to β 或 α holds if and only if B holds