Identifier     sap_keyword_set

 Purpose        Check if a keyword is set. The difference to IDLs keyword_set
                is that a value of zero is allowed and that the string 'NONE'
                is interpreted as 'not set'.

 Synopsis       set=sap_keyword_set(key)

 Arguments      Name      I/O  Type      Description
                -----------------------------------------------------
                key        I   keyword   the keyword to check
                
 Returns        0 if keyword is not set or if its value is 'NONE',
                1 else

 Description    To explicitly un-set a keyword use the string 'NONE' as value.
                Caution: case and blank sensitive!

 Comment        ---

 Example        if sap_keyword_set(det) then .....

 Dependencies   CALLS: --
                CALLED FROM: general auxillary routine

 Category       ISAP

 Filename       sap_keyword_set

 Author         E. Sturm (--> ES)

 Version        1.0

 History        0.1   20-10-95  ES    
                1.0   30-11-95  ES  V1 delivery
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Copyright (C) 1995, Max-Planck-Institut fuer extraterrestrische Physik (MPE);
                    Garching, Germany                                       ;
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