why it said the “The left recursion has been removed at the cost of an extra non-terminal symbol(E1) and a little extra complexity”?

When I read the book “A Practical approach to compiler construction” the chapter 4 “approaches to syntax analysis” and the section Left Recursion, it says:

“The left recursion has been removed at the cost of an extra non-terminal symbol”

I have no idea why say that, since $ A_1$ still contain recursion?


Von Neumann algebra such that every state is normal- what can be said about its dimension? What about the other direction?

This is exercise 5 in page 130 of Masamichi Takesaki ‘s Theory of Operator Algebras 1 (TO SHOW THAT IT IS FINITE DIMENSIONAL, AND THAT THE IFF HOLDS).

I know that now every state is weakly continuous on the unit ball. Maybe that means that it must be separable, and then I can show that it is finite dimensional?

Thanks in advance!

Someone said they have my ip and my internal ip. They threaten to post it on the internet. What should I do? [duplicate]

This question already has an answer here:

  • Is publishing your public IP address a security threat? 4 answers

They threatened me with a “I have your up and your internal up. I’m going to send it on the internet unless you do exactly as I say” what should I do? I’m doing what they say but I’m petrified.

What is the best terminology to use on a modal’s buttons when a user is about to leave said page?

I hope this question is not too banal. I would like to use the best terminology for a modal’s buttons.

Context: I’m building a feature for an administrative tool. The feature is on a customer profile’s dashboard which contains items that link to other administrative tools ultimately sending the admin outside of the customer’s profile. (Changes are saved every time an Admin makes a change so there’s no risk to lose progress)

When the Admin clicks on the item, a modal pops up and says “You’re about to leave this profile to x page. Are you sure you want to leave?”

Option for buttons Stay on Page Continue | Cancel Continue | Cancel yes

Is there one in particular that is more commonly used? thank you for your time.

Creating a twitter search link that references the user that clicked on said link

I was wondering if its possible to make a link of the formhttps://twitter.com/search?q=itunes.apple%20from%3A&src=typd where the search is performed on the whoever is logged in when it is clicked. In other words, is it possible to make the from: field auto populate itself using the current user’s @ username.