Example 1:
> f=sin(x);
> f;
sin(x)
> rename(x,y);
> f;
sin(y)
Example 2:
> a=1;
> f=sin(x);
> rename(x,a);
> a;
a
> f;
sin(a)
Example 3:
> verbosity=1!;
> f=sin(x);
> rename(y,z);
Warning: the current free variable is named "x" and not "y". Can only rename the free variable.
The last command will have no effect.
Example 4:
> rename(x,y);
> isbound(x);
false
> isbound(y);
true