W:=f(g(x))   
   f(g(x))   
   Means in expression W one can identify   
   a sub expression g(x) that depends of x and in W there is no other   
   subexpression that depends from x   
   out the expression g(x)   
   and f=subst(W, g(x)=y)   
   If I have a expression that contain   
   x, x is the first possible g(x)=x   
   so g(x) has to be different of x   
   because otherwise we would obtain   
   The same f() in W   
      
   Yes this is perhaps too much complex   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)