quiz about symbolic manipulation

[Carl Banks]

Michele Simionato wrote:
> In order to be specific I will pick up an example. Consider for instance 
> the expression
> 
> e="square(square(x+y)+z)+square(x+w)"
> 
> I would like to define a function
> 
> def substitute(math_expr,**subs):
>    #.... something here
>    result result
> 
> such that when I call
> 
> print substitute(e, square="x -> x**2")
> 
> I obtain
> 
> "((x+y)**2+z)**2+(x+w)**2"
> 
> The difficult part is that e can contains arbitrarily nested invocations
> of square: notice for instance that Mathematica is unable to solve this:
> 
> $ math
> Mathematica 4.1 for Linux
> Copyright 1988-2000 Wolfram Research, Inc.
> -- Motif graphics initialized --
> 
> In[1]:= square[square[x+y]+z]+square[x+w]/.square[x_] -> x^2
> 
>               2                      2
> Out[1]= (w + x)  + (z + square[x + y])
> 
> ________________________________________________________________________
> 
> If somebody is idle with nothing to do, he/she could think a little
> about that ;-)


Ok.  Try this:

square[square[x+y]+z]+square[x+w] //. square[x_]->x^2

Notice the //. instead of /.


-- 
CARL BANKS