Forms I-688, I-688A and I-688B are older employment authorization documents. These are no longer issued and have now expired.The same as I-766. 
FYI
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                    What is I-766? Thanks.
                     -Diva311- 
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                        06/04/2009 postreply
                                                17:02:44
                    
                    
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                    read my post again, Thanks.
                     -usedtobeadoctor- 
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                        06/04/2009 postreply
                                                17:13:19
                    
                    
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                    EAD or Perm?
                     -Diva311- 
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                        06/04/2009 postreply
                                                17:16:41