All is now working. It helps if the position vectors are
sensible which

>  position {<0,0,1>,<1,0,1>,<1,0,0>}

is not

Thanks to everyone who gave suggestions.

Gail
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* gsh### [at] monotixcoza                *   Step into the abyss,           *
* http://www.rucus.ru.ac.za/~gail/   *   and let go.        Babylon 5   *
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* The difficult we do immediately, the impossible takes a little longer *
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