🚀 go-pugleaf

I have a Prolog-predicate that gives me the n'th element of a list:

% list_index(List,Index,Element)

list_index([Head|_],1,Head).
list_index([_|Tail],Index,Elt) :-
	Index>1,
	NewIndex is Index-1,
	list_index(Tail,NewIndex,Elt).

This works fine for finding the element when the list and the Index are known
(instanciated), but I also want to use the same predicate to find the index
(that is the first one) when the list and the element are known. My predicate
doesn't work because of the 'is'-operator. Of course, I can use two different
predicates, but I have a feeling that it is possible with only one predicate
and some fine Prolog-code. Any suggestions anyone? Thanks in advance.

Jostein.

-- 
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* Jostein Baustad                    * E-mail : baustad@idt.unit.no           *
* Norwegian Institute of Technology  *          baustad@solan.unit.no         *
* Division of CS and Telematics      * "Reality is just a convenient          *
* Information and Knowledge Systems  *  measure for complexity."              *
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*             Queen's Park Rangers F.C. - SuperHoops !                        *
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