# Math From Scratch 0002: Set Theory

Part two in our tri-weekly series is here. This week’s topic: Set Theory. For past topic, click the “math from scratch” tag below. There will be too many of these to include links in every article.

## 13 replies on “Math From Scratch 0002: Set Theory”

1. Regarding the word “tri-weekly”. According to dictionary.com, it can mean either (1) every three weeks or (2) three times per week. In this case it’s obviously every three weeks, but is there an unambiguous way to say it with just a word or two?

2. matthewd says:

How about one and half fortnightly? Four words I know, but certainly less ambiguous…

• When it’s all said and done, there may be over a thousand of these. I’m sure I’ll eventually try every conceivable iteration (coming every 1814400 seconds!) by the time it’s all done. I should be wrapping up writing lesson 15 this weekend, and I’ve got the prerequisites mapped for 130 lessons.

3. matthewd says:

If you are partial to rounder numbers, try “every 1,500,000 micro-fortnights”.

4. ashaw says:

I would like to comment here that you have used & rather than the correct symbol ∧ thorough out this document. You may want to either correct the definitions in part 001 or here. but in keeping with logical notation conventions you may prefer ∧.

5. ashaw says:

I would like to comment here that you have used & rather than the correct symbol ∧ thorough out this document. You may want to either correct the definitions in part 001 or here. but in keeping with logical notation conventions you may prefer ∧. the latex for this is \vee.

• I missed that when I fixed lesson one; I’ll take care of it this weekend. (Also, the LaTeX is \wedge for this direction.)

• LaTeX? I thought that had gone the way of the slide rule. Is it still being used in academia?

• LaTeX is still quite popular where a lot of mathematical typesetting is required. Highly adaptable, very complete, and entirely keyboard driven are all big positives in my book. All of the lessons I’ve written are in LaTeX.

• ashaw says:

I apologize for this. I do hope that you use /wedge rather than & as this will allow people to read other literature on these subjects without unfamiliar notation, though I do understand the annoyance.

• You don’t have to apologize. I originally used this notation because that’s what my (dated and varied) resources used most often. Had I remembered using it in lesson two, I’d have fixed it there, too, when I fixed lesson one. I’ll get in and fix it later this week.

6. cab says:

Another minor correction. In section 3.1, spanning pages 2-3, you have this: “The straight horizontal line allows the two objects being compared to be equal in both cases, while the shape which opens to the right implies intuitively that the object on the right of the relation may be somehow larger or greater than the object on the right.” I think you mean the object of the right may be larger/greater than the object on the left.

7. cab says:

Another small one: in section 3.2, condition 1, it says A is a subset of B, put uses the proper subset symbol (sideways U without a line under it).