%N equals %F $MIR/src/subs/match.for
%D Check if input equals one of a number of possible strings
%P bpw
%: strings
%B
      logical function equals ( input, valid_strings )
      character*(*) input
      character*(*) valid_strings
      character*80  to_match

 Equals checks if the input string occurs in the comma-separated list of
 strings given by valid_strings. This effectively replaces a statement like
 "if(x.eq.'a'.or.x.eq.'b'.or.x.eq.'c'.or.x.eq.'d')" with
 "if(equals(x,'a,b,c,d'))".

 Input:
   input:         the string of which it has to be checked if it matches
   valid_strings: a comma-separated list of valid input strings
