I almost forgot to write my blog last week, although I have lots of questions because of our assignment.
It was a complicated assignment that we spend half of our day dealing with those confusing problems.
Fortunately we solved all the problems at the end.
I still want to know if the symbol "∃". Is that mean "there exists at least" or there is no "at least"? It is a little confusing to me.
I still have a question left, it was from last week's tutorial handout.
It's the g of question 1 from the handout.
"Some courses have the same prerequisites."
If I rewrite this symbolically as
"∃ y1,y2 ∈ C, ∃ x ∈ C, P(x,y1) ∧ P(x,y2)"
Is that also OK?
If I meet a question like this in the future test, I am afraid theta I will rewrite the question as above.
Good post.
回复删除"there exists" means ""there exists at least one" sine if there does not exit at least one then there does not exist!
As for your second question, lets look at the difference between the two answers. the answer provides in
exists x in C, exists y in C, such that for all z in C, P(z, x) iff P(z, y)
intuitively this means exactly what the english statement is saying. There are two courses in this set that for any other course, if it is a pre requisite for one it is also a prerequisite for the other.
Now if I look at your proposed solution what it is actually saying is "there are two courses that have at least one pre requisite in common"
If you're having trouble seeing the difference still come talk to me after tutorial and we'll figure it out.
Hope that helps.