World: r3wp

A negate.

ah yes. :-D

lol

It's the same as typing only  "2 3"

The 2 is evaluated (to 2), then the 3 is evaluated and returned, 
because it's last.

-2 3
 instead

Anton: that's it. So then  "+ 2 -3"

(Steeve, yes, more similar.)

- is the (only?) operator which cannot be used infix.

Sorry, that's an incorrect statement.

To get list of operators:

>> ? op!

Kib but for our sake, there is an infix version of - operator: subtract

You mean prefix.

- cannot be used as binary prefix operator, unlike the others + * 
/

Yes.

Steeve : thanks, i was just lookin for something like that

i don't like this name by the way, Carl should have renamed it: sub, 
since long time ago

I never use SUBTRACT because it's too long ! :-)  I always just use 
parens to allow me to use -, even if evaluation is slower.

Steeve : +1

Using parens, it's more clear this way.

sub suuuuuuuuuuuuuuuub ;-)

like in rebcode

Most operators have prefix only twins (that are called actions). 
Like: equals? is the twin of =

equal?

(without s)

multiply, add, subtract, divide, remainder, lesser?, lesser-or-equal?, 
not-equal?, equal?, strict-equal?, same?, greater?, greater-or-equal?

Geomol: power

beware with same? it's not really a math operator

If you prefer SUB instead of SUBTRACT, just do this in the beginning:

sub: :subtract

ah yes, POWER aslo.

*also*

I think, SAME? is like =?

yes but it's used for serie manipu

or objects, not for maths

>> [a b c] = [a b c]
== true
>> [a b c] == [a b c]
== true
>> [a b c] =? [a b c]
== false

oh my.... you should not bother Kib with same? too early ;-)

lol, he's bright, so he get it.

>> 1 = 1.0  
== true
>> 1 == 1.0
== false

Remember, if you wanna know more about operators like =, == and =?, 
just use ? to ask about them:

>> ? =?

It's fun doing these REBOL School sessions. It helps refresh the 
memories of us more experienced coders. It's hard (impossible) to 
remember all the corners of REBOL.

Geomol: in the last case 1 and 1.0 are different beasts because the 
first is integer and not the other, that's it ?

Can we use complex numbers ?

REBOL is like a little magical mountain lake. It doesn't look much 
on the surface, but it's soo deep.

yes Kib2 but the doc is incomplete, == is also case sensitive
>>"a" = "A"
==true
>>"a" == "A"
==false

kib, yes. == wants both to be same value and same datatype.

kib, you can implement complex numbers as two numbers inside a block.

or should i say, = is not case sensitive

kib, I've made a little library for complex numbers, if you like.

Geomol: I don't need them for starting, but maybe I'll have to use 
them later on. Where is it located ?

http://www.fys.ku.dk/~niclasen/rebol/libs/math/complex.r

Just a little start, and no documentation, so you have to read the 
code to figure it out.