EECS 203 W12, EXAM #1 STUDY GUIDE

This study guide aims to cover every topic that will be on the exam. Useful for studying and our one page of notes. Send it around!

What's on the exam?

• Homeworks 1 through 5
• Lectures 1 through 10
• Chapter 1, sections 2.1 through 2.5, sections 5.1 and 5.2

Propositions and operations

• Proposition = either true or false, but not both.

• ¬p = Negation of p
• p ∧ q = and (remember that ∧ is like the A in "AND")
• p ∨ q = or
• p ⊕ q = Exclusive or; XOR; only one can be true

• Tautology = always true

• Distributive laws
• p ∨ (q ∧ r) ≡ (p v q) ∧ (p v r)
• p ∧ (q v r) ≡ (p ∧ q) v (p ∧ r)
• De Morgan's Laws
• ¬(p ∧ q) ≡ ¬p v ¬q
• ¬(p ∨ q) ≡ ¬p ∧ ¬q

Conditionals

• p → q: if p, then q
• T → F = F; everything else is true

• Logical equivalencies
• p → q ≡ ¬p v q
• p → q ≡ ¬q → ¬p
• p v q ≡ ¬p → q
• p ∧ q ≡ ¬(p → ¬q)
• ¬(p → q) ≡ p ∧ ¬q
• (p → q) ∧ (p → r) ≡ p → (q ∧ r)
• (p → r) ∧ (q → r) ≡ (p v q) → r
• (p → q) v (p → r) ≡ p → (q v r)
• (p → r) v (q → r) ≡ (p ∧ q) → r

• Biconditional logical equivalencies
• p ↔ q ≡ (p → q) ∧ (q → p)
• p ↔ q ≡ ¬p ↔ ¬q
• p ↔ q ≡ (p ∧ q) v (¬p ∧ ¬q)
• ¬(p ↔ q) ≡ p ↔ ¬q

Quantifiers

• ∀x P(x) = P(x) is true for every x on the domain
• ∃x P(x) = there is an x on the domain for which P(x) is true
• ∃! x P(x) = there is ONLY ONE x on the domain for which P(x) is true

• De Morgan's Laws
• ¬∃x P(x) ≡ ∀x ¬P(x)
• ¬∀x P(x) ≡ ∃x ¬P(x)

• Nested quantifiers
• ∀x ∃x Q(x) ≡ ∀x (∃x Q(x))

• Quantifying two variables
• ∀x ∀y P(x, y) ≡ ∀y ∀x P(x, y) = true when P(x, y) is true for every pair of x and y
• ∀x ∃y P(x, y) = true when for every x, there is a y for which P(x, y) is true
• ∃x ∀y P(x, y) = true when there is an x for which P(x, y) is true for every y
• ∃x ∃y P(x, y) ≡ ∃y ∃x P(x, y) = true when there's a pair x,y for which P(x, y) is true

Rules of inference

• For propositional logic
• [p ∧ (p → q)] → q (modus ponens)
• [¬q ∧ (p → q)] → ¬p (modus tollens)
• [(p → q) ∧ (q → r)] → (p → r) (hypothetical syllogism)
• [(p v q) ∧ ¬p] → q (disjunctive syllogism)
• p → (p v q) (addition)
• (p ∧ q) → p (simplification)
• [(p) ∧ (q)] → (p ∧ q) (conjunction)
• [(p v q) ∧ (¬p v r)] → (q v r) (resolution)

• For quantifiers
• ∀x P(x) → P(c) (universal instantiation. Example: "All women are wise", therefore "Lisa is wise.")
• P(c) for arbitrary c → ∀x P(x) (universal generalization)
• ∃x P(x) → P(c) for some c (existential instantiation)
• P(c) → ∃x P(x) for some c (existential generalization)

Proofs

• Proof by exhaustion: try everything (only works with a finite number of possibilities)
• Proof by cases: you can break things into groups and show that certain groups work
• Proof by implication
• Assume P is true
• Assume P, P then Q, therefore Q
• Holds because if P is true you get Q and if P is false then Q is automatically implied
• After you prove Q it is no longer safe to assume P still holds
• Prove the contrapositive
• Assume Not Q show that it implies Not P
• Proving "if and only if"
• Prove each implies the other
• P implies Q AND Q implies P
• Construct a chain of iffs
• Show P iff R iff S iff Q so P iffQ
• Show that if the premise is T or F then something F would be T
• Example: Show that if P is false, then 0=2 since 0!=2 P must be true

Sets

• A collection of of objects called elements grouped together
• Ordering is not important, just which elements are contained
• ex. {x,y} is the same as {y,x}
• x ∈ D shows x is an element of D
• Special sets
• φ = the empty set = {}
• N = natural numbers = { 0, 1, 2, ... }
• Z = integers = { ... -2, -1, 0, 1, 2, ... }
• Z+ = positive integers = { 1, 2, 3, 4, ... }
• Q = rationals
• R = reals
• R+ = positive reals
• C = complex numbers
• Sets can contain other sets denoted S⊆T showing S is a subset of T or all the elements in S are in T
• Unioning (∪) two sets combines all the elements of two sets (additive)
• Intersection (∩) creates a set containing all elements contained by both sets
• Subtraction (–) creates a set containing only elements of either on or the other set but not both
• The compliment of a set is everything except the elements in that set
• A set has a cardinality equal to the number of elements in the set
• Power set
• The set of all sets in a set (I know, kind of strange wording)
• ex. B∈P({1,2}) iff B = {∅},{1},{2},{1,2}
• Cartesian product of sets
• Gives all possible sets of which the first element comes from set one and the second element comes from set 2
• Notation for defining a set
• A = { n ∈ R | x^3-3x+1 > 0 }
• Set equality
• Two sets are equal iff every element in one set is in the other and visa versa

Induction

• Principal