def <result> = fold <index> = <start> to <end> [ with <variable> [ = <init> ] ] [ while <condition> ] do <expression>;
<value1> is <greater/less> than or equal to <value2>
<value1> is [not] equal to <value2>
1. This reserved word is used to define an interval to be used when calculating the
fold function. For more information, see the
fold reserved word article.
2. This reserved word is also used with is operator in combination with word