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