## Why is {a^nb^n | n >= 0} not regular?

What you’re looking for is Pumping lemma for regular languages. Here is an example with your exact problem: Examples: Let L = {ambm | m ≥ 1}. Then L is not regular. Proof: Let n be as in Pumping Lemma. Let w = anbn. Let w = xyz be as in Pumping Lemma. Thus, xy2z … Read more

## What does ‘predicate’ mean in the context of computer science? [duplicate]

A predicate (‘PRED-i-cat’) is the part of a sentence that contains the verb and tells you something about the subject. For instance, in the sentence “Mike is eating”, we have the subject, ‘Mike’, and the predicate, ‘is eating’. In the context of computer science, we aren’t interested in stating a fact, but rather, in testing … Read more

## What exactly is the halting problem?

EDIT (much later than original answer): MarkCC of Good Math, Bad Math recently wrote up an excellent discussion of the Halting problem with concrete examples. The halting problem is basically a formal way of asking if you can tell whether or not an arbitrary program will eventually halt. In other words, can you write a … Read more

## Significant new inventions in computing since 1980

The Internet itself pre-dates 1980, but the World Wide Web (“distributed hypertext via simple mechanisms”) as proposed and implemented by Tim Berners-Lee started in 1989/90. While the idea of hypertext had existed before (Nelson’s Xanadu had tried to implement a distributed scheme), the WWW was a new approach for implementing a distributed hypertext system. Berners-Lee … Read more

## What does the quote “An extra level of indirection solves every problem” mean? [closed]

Generally it means that by increasing the level of abstraction one can make the problem easier to understand/resolve. Be careful with your abstractions though, the full quote at least as I heard it is, “You can solve every problem with another level of indirection, except for the problem of too many levels of indirection”.

## What are the differences between NP, NP-Complete and NP-Hard?

I assume that you are looking for intuitive definitions, since the technical definitions require quite some time to understand. First of all, let’s remember a preliminary needed concept to understand those definitions. Decision problem: A problem with a yes or no answer. Now, let us define those complexity classes. P P is a complexity class … Read more

## Computer architecture calculation values

The value is in the brackets. The registers in the brackets should be represented by their values too.

## How to analyze please Student voting system?

I think you can just have an id that automatically increments and make it your primary id. Then, your checking should be to check the student number and syearid and status before allowing the student to vote. with that you can just have 1 table for the vote records.