FUNCTION :  qseries[qbin] - the q-binomial coefficient        
                            (aka the Gaussian polynomial)
    
CALLING SEQUENCE :  qbin(q,m,n);
    
PARAMETERS :   q   - variable
               m,n - positive integers
   
SYNOPSIS :   
   
 When 0 < m <  n then qbin(q,m,n) returns the Gaussian polynomial       
        =   =
                                          (q)
                           [ n ]             n
                           [   ]   =   -----------
                           [ m ]       (q)  (q)        
                                q         m    n-m


otherwise it returns 0.

EXAMPLES :   
   
> qbin(q,3,6);   

               2            4    3    2            3    2
             (q  - q + 1) (q  + q  + q  + q + 1) (q  + q  + q + 1)
> expand(%);

            9    8      7      6      5      4      3      2
           q  + q  + 2 q  + 3 q  + 3 q  + 3 q  + 3 q  + 2 q  + q + 1

SEE  ALSO :  aqprod