Welcome to the month of March! For Friday:
- Group presentation day — be prepared.
- Your quiz will be a constructive existence proof, and will involve rational/irrational numbers. Study appropriately (see your groupwork, and read Hammack 7.3-7.4). Here are a couple similar types of proofs appropriate to study by:
- For every irrational x, there exists an irrational y such that xy = 1.
- For every two rational numbers x and y, there is an irrational between x and y (we did this one before).
- Every rational number can be written as a product of two rational numbers.
Have a great weekend, all! For Monday, please:
Also, some people asked about how to include a picture in latex. The short story is to make sure your preamble where you include packages includes the package:
And then include a picture where you want it in your document by putting (in text mode, on its own line, surrounded by empty lines):
You can find more info about this online, for example here. You can adjust the width to make your picture bigger or smaller. You can include jpg, png or pdf files, among others. You can put it inside a “figure” environment if you want it to “float” and position itself with a caption (see link above).
In class on Monday, we covered truth tables and logical implication, including the notions of contradiction and tautology. We used a handout of truth-tables and played a logic game (instructions and cards).
For Wednesday: (links below are coming shortly)
- Fill in the truth table handout. Lines 3 and 4 (each a single table) are each a demonstration (proof, actually!) of a certain logical equivalence. Write down what the logical equivalence is, and then compare to the solutions.
- Read Hammack, 2.6, again. At the bottom of page 50 are a list of useful logical laws. Please become familiar with these by using them to simplify statements. Here is a worksheet you should complete for practice and bring to class.
- Learn the meaning of the word converse on page 44 of Hammack.
- Read Hammack, Chapter 5 until the end of 5.1 (pages 102-105). From this, learn the meaning of the word contrapositive.
- Take a look at these solutions to Proof Quiz #4, and compare to your proof. (Grading note: I haven’t decided what to do about proof quiz #3 yet.)
- In class Wednesday, we will take up the homework above, and then do something fun and educational.
Happy Valentine’s Day!
Important Grading Clarification:
- In the Canvas spreadsheet, grades for badges are recorded as
- 0 (no credit)
- 1 (partial)
- 2 (full)
- This differs from the very first quiz, where they were marked on your paper 0, 1/2, 1. But it became apparent that having integers instead of fractions in the spreadsheet on canvas was preferable. Your papers from Badges Quiz #2 and onwards are marked 0, 1, 2.
- There is no extra credit for badges.
- Make absolutely sure you are in contact with your new group-mates and have a plan for Friday. Go to Canvas, click on “People”, then “Groups”. You can contact your group via Canvas.
- Please complete the worksheet Negation I that we began in class. (Note: there was a typo on the sheet handed out in #7, 8, 9, where “shoes” at the end should have been “hat”. This is now corrected.)
- Watch this two-minute video about “if-then” statements.
- Optional: if you are curious about the studies I mentioned in class, here’s some reading:
PROOF QUIZ #3 RE-DO ANNOUNCEMENT!
- I realized when administering the quiz on Friday that it was confusing what I was after, in terms of what you can and cannot use. That’s poor quiz design on my part. Therefore we’ll have a “re-do”.
- You can download a copy of the quiz, print it out, and write up your best proof for handing in on Monday. This will replace your in-class quiz for grading. This is optional (if you don’t hand something in, I’ll use the quiz you handed in in class). The new copy of the quiz (at the link above) has better instructions on what you can use or not use. You can also email me for clarifications.
- For this re-do, it is a violation of the honor code to work together, or use the help of a tutor or friend or any outside source, including the internet. You can, however, use your course notes and textbook. There is no time limit besides the deadline for hand-in, which is in class Monday.
- We are reshuffling groups. I am forming new groups using the survey you completed on Canvas about group preferences. (If you didn’t complete the survey, you must have forgotten to read the website before Friday’s class. You’ll be assigned to groups randomly in that case.) The new groups will be formed on canvas and you can check them by logging in. You can now log in to canvas to find your new groups. You should also be able to contact one another there.
For Monday’s class:
- Re-do your Proof Quiz #3 as described above if you desire (optional).
- Contact your new groups to schedule a time for this week’s groupwork.
- Please read Hammack, Sections 4.4 and 4.5, and do exercises 14-17 (compare with solutions to 15, 17 in the back). This deals with the topic of “cases” and the use of the phrase “without loss of generality” (also known as WLOG). These will come up naturally in future, but for now I’ll consider them covered by your reading in the book, at least in the sense that you are familiar with them, if not a master of them.
- In class, we will work on negation and introduce truth tables.
- There will be a badges quiz, and the available badges will be the same as last time. A good goal for this quiz is to finish off any Sets badges you have not yet earned, and then focus on Proofs I if you have room for more. For example, 70% of students have earned Sets I, and so I’ll probably stop including it in badges quizzes in a couple weeks (I will warn you before the last chance). The Logic IV badge is material we will cover soon, but is still a bit “ahead” of where we are.
NOTE: Thursday’s office hour has to end slightly early, as I mentioned before. It will end by 1:45 but possibly I have to go at 1:40.
For class friday:
- It is group presentation day, don’t forget.
- We’ll make new groups! Please fill out this form (to get to it, go to Quizzes on Canvas) on your groupwork preferences. I will try to do some “roommate matching” based on your feedback for creating the next groups.
- The proof quiz will be a proof by contradiction. It will be in the style of Hammack Chapter 6, exercises 2, 3, 9, 11, and the proofs by contradiction you have seen in class or your groupwork assignments.
- Study for your proof quiz. Here are some tips on how. I suggest you study by examining the proofs just mentioned above. The study goal is to understand the structure of the proofs so that you can reproduce them without aids. It’s important not to memorize, however, as a memorized proof is of limited value compared to one you can reproduce from understanding its structure and principles. One tip here is to focus on giving an explanation of how to build the proof, instead of giving the proof itself. Don’t memorize sentence-by-sentence but instead focus on how you would explain the process of discovering the proof (for example, the process of working backwards from your goal, or unravelling a definition). (I do my best to model this behaviour in class, to give you some examples.)