I'm reading Hennessy and Patterson's Computer Architecture: A Quantitative Approach, and I've come across a strange upside-down-'A' like symbol in some pseudo-code describing Tomasulo's Algorithm (I can't even find it in my character map). It's followed immediately by an 'x' and an if statement enclosed by parentheses. I'm guessing it's some sort of function?

Here's the context:

<upside-down-A-thing>x( if(RegisterStat[x].Qi=r){Regs[x] <- result; RegisterStat[x].Qi <- 0} );

What does it mean?

## Meaning of an upside down A symbol

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### Re: Meaning of an upside down A symbol

It's called the universal quanitfier and it means "for all values of x in the domain".

http://en.wikipedia.org/wiki/Universal_quantification

http://en.wikipedia.org/wiki/Universal_quantification

### Re: Meaning of an upside down A symbol

And for future reference, since you'll surely run across it in the future, a backwards E represents the existential quantifier meaning, "there exists a value x" which fulfills the given statement.

- DubioserKerl
**Posts:**71**Joined:**Sat Jun 07, 2008 8:23 am UTC

### Re: Meaning of an upside down A symbol

Yeah.

And keep in mind: The backwards E means there exists at least one x in the domain that fulfills the statement afterwards. So, a statement that fulfills

FORALL x statement(x)

fulfills also

EXISTS x statement(x) as long as there exists one x.

If there are no values in the domain (that can happen if you have nested statements),

FORALL x statement(x)

is also true, but

EXISTS x statement(x)

is obviously not.

DK

And keep in mind: The backwards E means there exists at least one x in the domain that fulfills the statement afterwards. So, a statement that fulfills

FORALL x statement(x)

fulfills also

EXISTS x statement(x) as long as there exists one x.

If there are no values in the domain (that can happen if you have nested statements),

FORALL x statement(x)

is also true, but

EXISTS x statement(x)

is obviously not.

DK

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