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 39.11.7 Comparison
 ------------------
 
 The procedures in this section are used for comparing strings in
 different ways.  The comparison predicates differ from those in R5RS in
 that they do not only return `#t' or `#f', but the mismatch index in
 the case of a true return value.
 
    `string-hash' and `string-hash-ci' are for calculating hash values
 for strings, useful for implementing fast lookup mechanisms.
 
  -- Scheme Procedure: string-compare s1 s2 proc_lt proc_eq proc_gt
           [start1 end1 start2 end2]
  -- Scheme Procedure: string-compare-ci s1 s2 proc_lt proc_eq proc_gt
           [start1 end1 start2 end2]
      Apply PROC_LT, PROC_EQ, PROC_GT to the mismatch index, depending
      upon whether S1 is less than, equal to, or greater than S2.  The
      mismatch index is the largest index I such that for every 0 <= J <
      I, S1[J] = S2[J] - that is, I is the first position that does not
      match.  The character comparison is done case-insensitively.
 
  -- Scheme Procedure: string= s1 s2 [start1 end1 start2 end2]
  -- Scheme Procedure: string<> s1 s2 [start1 end1 start2 end2]
  -- Scheme Procedure: string< s1 s2 [start1 end1 start2 end2]
  -- Scheme Procedure: string> s1 s2 [start1 end1 start2 end2]
  -- Scheme Procedure: string<= s1 s2 [start1 end1 start2 end2]
  -- Scheme Procedure: string>= s1 s2 [start1 end1 start2 end2]
      Compare S1 and S2 and return `#f' if the predicate fails.
      Otherwise, the mismatch index is returned (or END1 in the case of
      `string='.
 
  -- Scheme Procedure: string-ci= s1 s2 [start1 end1 start2 end2]
  -- Scheme Procedure: string-ci<> s1 s2 [start1 end1 start2 end2]
  -- Scheme Procedure: string-ci< s1 s2 [start1 end1 start2 end2]
  -- Scheme Procedure: string-ci> s1 s2 [start1 end1 start2 end2]
  -- Scheme Procedure: string-ci<= s1 s2 [start1 end1 start2 end2]
  -- Scheme Procedure: string-ci>= s1 s2 [start1 end1 start2 end2]
      Compare S1 and S2 and return `#f' if the predicate fails.
      Otherwise, the mismatch index is returned (or END1 in the case of
      `string='.  These are the case-insensitive variants.
 
  -- Scheme Procedure: string-hash s [bound start end]
  -- Scheme Procedure: string-hash-ci s [bound start end]
      Return a hash value of the string S in the range 0 ...  BOUND - 1.
      `string-hash-ci' is the case-insensitive variant.
 

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