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+;;;;            Generic sequence operations
+
+;;; There are many kinds of data that can be used to represent sequences: 
+;;;     examples include strings, lists, and vectors.
+
+;;; There are operations that can be defined for all sequence types.
+
+;;;                    Constructing
+;;;
+;;; (sequence:construct <sequence-type> <item-1> ... <item-n>)
+;;;    Constructs a new sequence of the given type and of size n with
+;;;    the given elements: item-1 ... item-n
+
+;;; (sequence:null <sequence-type>)
+;;;    Produces the null sequence of the given type
+
+
+;;;                     Selecting
+;;;
+;;; (sequence:ref <sequence> <i>)
+;;;    Returns the ith element of the sequence.  We use zero-based
+;;;    indexing, so for a sequence of length n the ith item is
+;;;    referenced by (sequence:ref <sequence> <i-1>).
+
+;;; (sequence:size <sequence>)
+;;;    Returns the number of elements in the sequence.
+
+;;; (sequence:type <sequence>)
+;;;    Returns the predicate defining the type of the sequence given.
+
+
+;;;                     Testing
+;;;
+;;; (sequence:null? <sequence>)
+;;;    Returns #t if the sequence is null, otherwise returns #f.
+
+;;; (sequence:equal? <sequence-1> <sequence-2>)
+;;;    Returns #t if the sequences are of the same type and have equal
+;;;    elements in the same order, otherwise returns #f.
+
+; ADDITION:
+;;; (sequence:elements-equal? <sequence-1> <sequence-2>
+;;;    Returns #t if the sequences have equal elements in the same order;
+;;;    the sequences do not have to be of the same type. Otherwise
+;;;    returns #f.
+
+
+;;;                     Mutation
+;;;
+;;; Some sequences are immutable, while others can be changed.  
+;;;
+;;; For those that can be modified we can change an element:
+;;;
+;;; (sequence:set! <sequence> <i> <v>) 
+;;;    Sets the ith element of the sequence to v.
+
+;;;                  Cutting and Pasting
+;;;
+;;;  (sequence:subsequence <sequence> <start> <end>)
+;;;    The arguments start and end must be exact integers such that 
+;;;       0 <= start <= end <= (sequence:size <sequence>).
+;;;    Returns a new sequence of the same type as the given sequence,
+;;;    of size end-start with elements selected from the given sequence.
+;;;    The new sequence starts with the element of the given sequence
+;;;    referenced by start.  It ends with the element of the given
+;;;    sequence referenced by end-1.
+
+;CHANGED:
+;;; (sequence:append <sequence-1> ... <sequence-n>)
+;;;    Returns a new sequence of the type of the first sequence, formed 
+;;;    by concatenating the elements of the given sequences.  The size of 
+;;;    the new sequence is the sum of the sizes of the given sequences.
+
+;;;                      Iterators
+;;;
+;;; (sequence:generate <sequence-type> <n> <function>)
+;;;    Makes a new sequence of the given sequence type, of size n.
+;;;    The ith element of the new sequence is the value of the 
+;;;    function at the index i.
+
+; CHANGED:
+;;; (sequence:map <function> <seq-1> ... <seq-n>)
+;;;    Requires that the sequences given are of the same size and
+;;;    that the arity of the function is n.  The ith element
+;;;    of the new sequence is the value of the function applied to the
+;;;    n ith elements of the given sequences.
+
+; CHANGED:
+;;; (sequence:for-each <procedure> <seq-1> ... <seq-n>)
+;;;    Requires that the sequences given are of the same size and
+;;;    that the arity of the procedure is n.  Applies the
+;;;    procedure to the n ith elements of the given sequences;
+;;;    discards the value.  This is done for effect.
+
+;;;                 Filtration and Search
+;;;
+;;; (sequence:filter <sequence> <predicate>)
+;;;    Returns a new sequence with exactly those elements of the given
+;;;    sequence for which the predicate is true (does not return #f).
+;;;
+;;; (sequence:get-index <sequence> <predicate>)
+;;;    Returns the index of the first element of the sequence that
+;;;    satisfies the predicate.  Returns #f if no element of the
+;;;    sequence satisfies the predicate.
+;;;
+;;; (sequence:get-element <sequence> <predicate>)
+;;;    Returns the first element of the sequence that satisfies the
+;;;    predicate.  Returns #f if no element of the sequence satisfies
+;;;    the predicate.
+
+;;;                    Accumulation
+;;;
+;;; (sequence:fold-right <function> <initial> <sequence>)
+;;;    Returns the result of applying the given binary function,
+;;;    from the right, starting with the initial value.
+;;;    For example, 
+;;;      (sequence:fold-right list 'end '(a b c))
+;;;           => (a (b (c end)))
+
+;;;
+;;; (sequence:fold-left <function> <initial> <sequence>)
+;;;    Returns the result of applying the given binary function,
+;;;    starting with the initial value, from the left.
+;;;    For example, 
+;;;      (sequence:fold-left list 'start '(a b c))
+;;;           => (((start a) b) c)
+
+
+