CLHS: Section 1.4.1.2.2

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## 1.4.1.2.2 Indirection in Modified BNF Syntax

An indirection extension is introduced in order to make this new syntax more readable:

O

If O is a non-terminal symbol, the right-hand side of its definition is substituted for the entire expression O. For example, the following BNF is equivalent to the BNF in the previous example:

`(x` [[``O``]]`y)`

    O::= A | B* | C

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