離散數學(3)

第三章 Set Theory

A set should be well-defined collection of objects. These objects are called elements and we said to be members of the set.

If C,D are sets from a universe U, we say that C is a subset of D and write C c D or D c C , if every element of C is an element of D. If , in addition, D contains an element that is not in C, then C is called a proper subset of D, and this is denoted by C c D

for A,B c U we define the flowing

a) A U B( the union of A and B) = {x|x ε A V ε B}

b) A∩B( the intersection of A and B) = {x| x ε A ^ ε B}

c)AΔB(the symmetric difference of A and B ) = {x| (x ε A V ε B) ^

x not ε A∩B}={x|x ε AUB ^ x not ε A∩B}