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Discrete Mathematics University of Kentucky CS 275 Spring ... - MGNet

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The textbook has a large number <strong>of</strong> set identities in a table.<br />

Identity<br />

Law(s)<br />

A2/ = A, A3U = A Identity<br />

A2U = U, A3/ = /<br />

Domination<br />

A2A = A, A3A = A<br />

Idempotent<br />

A = A<br />

Complementation<br />

A2B = B2A, A3B = B3A<br />

Commutative<br />

A2(B2C) = (A2B)2C, A3 (B3C) = (A3B) 3C Associative<br />

A3 (B2C) = (A3B) 2 (A3C)<br />

Distributive<br />

A2(B3C) = (A2B) 3 (A2C)<br />

A!B = A"B, A!B = A"B<br />

DeMorgan<br />

A2 (A3B) = A, A3 (A2B) = A<br />

Absorption<br />

A!A = U, A"A = #<br />

Complement<br />

Many <strong>of</strong> these are simple to prove from very basic laws.<br />

31<br />

Definition: A function f:A%B maps a set A to a set B, denoted f(a) = b for a,A<br />

and b,B, where the mapping (or transformation) is unique.<br />

Definition: If f:A%B, then<br />

• If (b,B )a,A (f(a) = b), then f is a surjective function or onto.<br />

• If A=B and f(a) = f(b) implies a = b, then f is one-to-one (1-1) or injective.<br />

• A function f is a bijection or a one-to-one correspondence if it is 1-1 and<br />

onto.<br />

Definition: Let f:A%B. A is the domain <strong>of</strong> f. The minimal set B such that<br />

f:A%B is onto is the image <strong>of</strong> f.<br />

Definitions: Some compound functions include<br />

n<br />

n<br />

• (!<br />

f<br />

i i )(a) = ! f (a) i=1 i . We can substitute + if we expand the summation.<br />

n<br />

n<br />

• (!<br />

f<br />

i=1 i )(a)=! f (a) i=1 i . We can substitute * if we expand the product.<br />

32

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