For the exam on Friday, it would help you to do the following things:
- Learn the definitions you needed to know for the quiz. Know the definitions precisely. You should know the statements in formal language, as well as interpretations in words. E.g., A\subseteq B means (\forall x)(x\in A \implies x\in B) and this can be read as "every element in A is also in B".
- Do "blank-paper practice" for the problems on the four problem sets that have been handed back. Note: You should be able to do all the problems, including the hard ones. Avoid repeating a mistake you made on the problem set.
- Understand these challenging concepts:
- \subseteq vs. \in vs. =
- A\subseteq B vs. A\cap B
- \P(A), the power set of A
- (\forall x)(P(x)) vs. \{\,x \mid P(x)\,\}
- ``For all x, \ldots'' vs. ``There exists an x where \ldots''
- (\forall x)(\exists y)(P(x,y)) vs. (\exists y)(\forall x)(P(x,y))
- P \wedge Q vs. A\cap B
- P(x) \implies Q(x) vs. \{\, x \mid P(x) \hbox{ and } Q(x) \,\}
- Know the negations of the various types of propositions we've studied.
- Know the contrapositive, converse, and inverse, and which ones are equivalent.
- Know how to translate English into formal logic and vice versa.
- Know how to use mathematical induction.
- Know the proofs of these key examples. You should not memorize them, but should remember the central idea(s) and reconstruct the proof from that memorized core.
- \emptyset\subseteq A for all A
- A\subseteq B iff \P(A)\subseteq\P(B)
- A\times B=\emptyset if, and only if, A=\emptyset or B=\emptyset
- For A\ne\emptyset and B\ne\emptyset, if A\times B\subseteq C\times D then A\subseteq C and B\subseteq D
- \sqrt{2} is irrational
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