[xsl] variable problem

["Kent Seegmiller" <hookjaw20@xxxxxxxxxxx>]

When I try to convert a variable to and integer i.e.
<xsl:variable name="gap" as="xs:integer" select="@end - @begin"/>
<xsl:for-each select="1 to $gap">
...
</xsl:for-each>
I get the error:
XPTY0004: Required type of second operand of 'to' is xs:integer; supplied 
value has xs:double

Why do I get this error and how can it be resolved?