FUNCTION :  eta2geta - convert from ETA to eta notation 

CALLING SEQUENCE :  eta2geta(etaexp)
                    
PARAMETERS :      etaexp - expression involving ETAnm and ETAn

SYNOPSIS :   
   This function does the following conversions:
        ETAnm(d,g) ->  eta[d,g](tau)                       
        ETAn(b) ->  eta(b*tau)                       

EXAMPLES :   
> with(qseries):
> with(thetaids):

> eta2geta();
-------------------------------------------------------------
eta2geta(etaexp)                                       
   This function is a notation conversion.                  
   It does the following                                   
        ETAnm(d,g) ->  eta[d,g](tau)                       
        ETAn(b) ->  eta(b*tau)                       
-------------------------------------------------------------

> EP:=ETAnm(5,1)/ETAnm(5,2):
> EP1:=ETAn(1):
> eta2jac(EP);
                                                          1/5
                                     JAC(1, 5, infinity) q
                                     ------------------------
                                       JAC(2, 5, infinity)
 
> eta2jac(EP1);
                                    (1/24)
                                   q       JAC(0, 1, infinity)
 
> eta2geta(EP);
                                          eta[5, 1](tau)
                                          --------------
                                          eta[5, 2](tau)
 
> eta2geta(EP1);
                                             eta(tau)
 

SEE ALSO :  eta2jac, jac2eprod