### 2.3 Other notations

For a description of the notations used for numbers, see section Numbers.

`. + -`
  These are used in numbers, and may also occur anywhere in an identifier except as the first character. A delimited plus or minus sign by itself is also an identifier. A delimited period (not occurring within a number or identifier) is used in the notation for pairs (section see Pairs and lists), and to indicate a rest-parameter in a formal parameter list (section see Procedures). A delimited sequence of three successive periods is also an identifier.
`( )`
  Parentheses are used for grouping and to notate lists (section see Pairs and lists).
`'`
  The single quote character is used to indicate literal data (section see Literal expressions).
```
  The backquote character is used to indicate almost-constant data (section see Quasiquotation).
`, ,@`
  The character comma and the sequence comma at-sign are used in conjunction with backquote (section see Quasiquotation).
`"`
  The double quote character is used to delimit strings (section see Strings).
`\`
  Backslash is used in the syntax for character constants (section see Characters) and as an escape character within string constants (section see Strings).
`[ ] { } |`
  Left and right square brackets and curly braces and vertical bar are reserved for possible future extensions to the language.
`#`
  Sharp sign is used for a variety of purposes depending on the character that immediately follows it:
`#t #f`
  These are the boolean constants (section see Booleans).
`#\`
  This introduces a character constant (section see Characters).
`#(`
  This introduces a vector constant (section see Vectors). Vector constants are terminated by `)` .
`#e #i #b #o #d #x`
  These are used in the notation for numbers (section see Syntax of numerical constants).