R4RS 4.1.2  (quote <datum>)  ==>  object

(quote <datum>)  ==>  <datum>
'<datum>         ==>  <datum>
<constant>       ==>  <constant>

`(quote <datum>)' evaluates to <datum>. <Datum> may be any external
representation of a Scheme object (see section see section 3.3
External representations). This notation is used to include literal
constants in Scheme code.

(quote a)         ==>  a
(quote #(a b c))  ==>  #(a b c)
(quote (+ 1 2))   ==>  (+ 1 2)

`(quote <datum>)' may be abbreviated as '<datum>. The two notations
are equivalent in all respects.

'a          ==>  a
'#(a b c)   ==>  #(a b c)
'()         ==>  ()
'(+ 1 2)    ==>  (+ 1 2)
'(quote a)  ==>  (quote a)
''a         ==>  (quote a)

Numerical constants, string constants, character constants, and
boolean constants evaluate "to themselves"; they need not be quoted.

'"abc"    ==>  "abc"
"abc"     ==>  "abc"
'145932   ==>  145932
145932    ==>  145932
'#t       ==>  #t
#t        ==>  #t

As noted in section 3.5 Storage model, it is an error to alter a
constant (i.e. the value of a literal expression) using a mutation
procedure like set-car! or string-set!.
