Date: Wed, 6 Feb 2002 21:56:35 +0100                                                                           
From: "Laudien, Joachim" <Joachim.Laudien@fujitsu-siemens.com>                                                 
To: "'gms2w@cs.virginia.edu'" <gms2w@cs.virginia.edu>                                                          
Subject: To Bug a Mockingbird                                                                                  
                                                                                                               
Hi,                                                                                                            
                                                                                                               
I think your Mockingbird applet is a very nice idea, but you seem to have some serious problems with variable  
clashes. E.g.                                                                                                  
       

BETA REDUCTION AREA                                                                                            
                                                                                                               
Beta Reducing Birds:                                                                                           
Mockingbird and Lark                                                                                           
La.aaLx.Ly.x(yy)                                                                                               
Lx.Ly.x(yy)Lx.Ly.x(yy)                                                                                         
Ly.Lx.Ly.x(yy)(yy)                                                                                             
Ly.Ly.(yy)(yy)                                                                                                 
Beta Reduction Complete                                                                                        
                                                                                                               
Renaming to try to match a known bird . . .                                                                    
La.La.(aa)(aa)                                                                                                 
                                                                                                               
The correct result would be (inserting some whitespace for clarification)                                      
                                                                                                               
Beta Reducing Birds:                                                                                           
Mockingbird and Lark                                                                                           
La.aa  Lx.Ly.x(yy)                                                                                             
Lx.Ly.x(yy)  Lx.Ly.x(yy)
Ly. Lx.Ly.x(yy) (yy) // renaming bound variable y in Lx.Ly.x(yy) to avoid clash with free y in (yy)
Ly. Lx.Lz.x(zz) (yy)
Ly. Lz.(yy)(zz)
Beta Reduction Complete

Kind regards,

Joachim Wolf Laudien