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qs26.sdy
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1995-10-31
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"Sets & Logic Chpt 1 (Sets)"
"The objects of a set are called...?"
"elements, points or members "
"Describe the following sets: N, Z, Q, R "
"N = Set of all positive integers
Z = Set of all integers
Q = Set of all rational numbers
R = Set of all real numbers "
"Two notations for defining a set are..."
"List notation
Set-builder notation "
"Describe the difference between 'membership' and 'inclusion'. "
"'membership' refers to the elements or objects that make up a set.
'inclusion' refers to one set being a subset of another."
"Define 'inclusion': "
"A is included in B, if and only if every member of A is a member of B."
"Define 'equality' between sets"
"
A equals B, if and only if A is a subset of B, and B is a subset of A.
or put another way...
if and only if every member of A is a member of B, and vice versa. "
"Comment on 'order' and 'repetition' within sets "
"The 'order' in which items appear in a list does not influence the
set made from that list.
The 'repetition' of items in a list does not influence the set
made from that list. "
"Explain 'subset' and 'superset'."
"A is a subset of B and
B is a superset of A
if and only if A is a subset of B"
"Define the empty set. "
"The empty set is a SUBSET of every set
but not a member of a set unless specifically listed. "
"Is the empty set an element of the empty set? "
"No. "
"Define a proper subset."
" A is a proper subset of B, if A is a subset of B but not equal to B
that is, B is not a subset of A."
"Define a singleton. "
"A set consisting of a single element. "
"Define a universal set. "
"A set including all the sets under discussion
usually it is a standard set, such as, N, Z, or R. "
"Define a union. "
"The union of A and B is defined to be
the set of all points x, such that x is in A or B or both. "
"Define the intersection of two sets. "
"The set of all points y such that y is in A and y is in B.
Thus, A intersection B is a subset of A and a subset of B
- if A and B have no elements in common, we call them DISJOINT
- if A and B have elements in common, we say they MEET. "
"Give an example of the commutative law for union and intersection. "
"A union B = B union A
A intersection B = B intersection A "
"Give examples of the associative law for union and intersection."
"(A union B) union C = A union (B union C)
(A intersection B) intersetion C = A intersection (B intersection C) "
"Give examples of the distributive law for
- union distributes over intersection
- intersection distributes over union."
"A union (B intersection C) = (A union B) intersection (A union C)
A intersection (B union C)=(A intersection B) union (A intersection C)"
"What is the first rule for proofs? "
"Go to the definitions & identify the targets "
"Define the RELATIVE COMPLEMENT of B in A (denoted A - B or A \ B ) "
"The set of all elements of A that are not elements of B
Also known as SET-THEORETIC DIFFERENCE"
"Define the CARTESIAN PRODUCT of A and B "
"The set of all ordered pairs (a,b) where a is in A, and b is in B
denoted as A x B
Note: the order matters... (2,3) is NOT = to (3,2)
so A x B is not the same set as B x A UNLESS A=B or
unless A or B is empty ( A x 0 = 0 ) 0=empty set"
"Does the Distributive Law apply to Cartesian Products ? "
" Yes
Generally speaking, however, the Cartesian Product is
neither Associative or Commutative. "
"Define the POWER SET of set X "
"The POWER SET is the set of all subsets of X
Note: P(0) = {0}
P({1, 2}) = {0, {1}, {2}, {1, 2}}
Note: the ELEMENTS of the Power set are SETS !!"
"What is the strategy for proofs ? "
" The last assertion or operation used to form the statement
is the DEFINITION we go to first."
"In the Cartesian Product of set A with itself, define the DIAGONAL "
" the set of all ordered pairs (a,a) as a runs over A
diagonal of {1,2,3} X {1,2,3} = {(1,1), (2,2), (3,3)} "