Well, the "else" part is cut&paste, so i'm not writing more code... but
the important here is the execution of code without necessity, so i'll
change to the choose/when/otherwise.

is very neat. However i cant use it cause the "otherwise" is not 0 but
instead the prior value of the node, that could be 1 or 0.

As a side question, i tend to make things like

<xsl:if test="parent::menu=(//menu)[$pos]">
<xsl:text>1</xsl:text>
</xsl:if>
<xsl:if

test="not(parent::menu=(//menu)[$pos])">

                           <xsl:text>0</xsl:text>
                       </xsl:if>

Is there any drawback in doing this insted of choose/when/otherwise?

Yes, you're writing more code and the XSLT processor is executing more code.

In fact, assuming you've got the boolean condition right, you could replace
this whole thing by

<xsl:value-of select="number(parent::menu=(//menu)[$pos])"/>

Michael Kay
http://www.saxonica.com/