error in Calabash running xslt with java extension functions.

hello,
 
I am trying to run an xslt (2.0) in a pipeline in Calabash. The xslt uses extension functions from java.lang.Math.
I get error messages like:
    XPath syntax error at char 10 on line 8 in {math:PI() div 180.}: Cannot find a matching 0-argument function named {java:java.lang.Math}PI()
and similarly
    Cannot find a matching 1-argument function named {java:java.lang.Math}cos()
etc.
 
I have used this xslt many times outside Calabash, just using Saxon, and then it works fine. I expected it to work in Calabash because it also uses Saxon.
 
Has anyone encontered this problem, or knows if this kind of direct Java use was deliberately disabled, or should I adapt some setting or....?
 
thanks, Egbert Gramsbergen
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Delft University of Technology