>consider the set of axis "y"
>against "f(x)".

The function f(x) must be monotone for that to make sense.
>
>the line "y=f(x)" is a straight
>line through the origin.

Yes. It's the first quadrant's diagonal.
>
>the line "y=x" is the inverse
>of f(x). i.e. "y=(f^-1)(f(x))".

Yes.

>reflect this in the 'straight line'
>"y=f(x)" and you get
>"y=f(f(x))", i think

Yes. That's true.

>this means that y=x reflected in
>y=f(x) gives y=ff(x)!

That's right, but why the exclamation mark?

>i realise that there's a problem
>with,for example f(x)=x^2 but i
>know that this comes from
>the squaring. it can
>be solved by reflecting y=mod(x)

That I do not know.

>sorry to bother you again, but
>thanx for your help.
>none of my tutors bother
>to help me.

So, what are they for?