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This section provides a formal syntax for Scheme written in an extended BNF.
All spaces in the grammar are for legibility. Case is insignificant;
for example, #x1A
and #X1a
are equivalent. <empty>
stands for the empty string.
The following extensions to BNF are used to make the description more concise: <thing>* means zero or more occurrences of <thing>; and <thing>+ means at least one <thing>.