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Conditionals

if <test> <consequent> <alternate> syntax
if <test> <consequent> syntax

Syntax: <Test>, <consequent>, and <alternate> may be arbitrary expressions.

Semantics: An if expression is evaluated as follows: first, <test> is evaluated. If it yields a true value (see section see Booleans), then <consequent> is evaluated and its value(s) is(are) returned. Otherwise <alternate> is evaluated and its value(s) is(are) returned. If <test> yields a false value and no <alternate> is specified, then the result of the expression is unspecified. 

(if (> 3 2) 'yes 'no)                  ==>  yes
(if (> 2 3) 'yes 'no)                  ==>  no
(if (> 3 2)
    (- 3 2)
    (+ 3 2))                           ==>  1