From hcc8471@garnet.acns.fsu.edu  Tue Jun 15 21:35:12 1999
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Date: Tue, 15 Jun 1999 15:35:12 -0400
From: Hongmei Chi <hcc8471@garnet.acns.fsu.edu>
Message-Id: <199906151935.PAA68860@garnet2.acns.fsu.edu>
To: prolog@swi.psy.uva.nl
Subject: Help


I try to write a simple program to define a plus by myself. 

sum(X,0,X).
sum(W, f(Y), f(Z)):-sum(W,Y,Z).

This doesnot work and just keep telling me to refine sum.
Please tell me the reason.

The goal of this program is to define sum(X,Y,Z) : Z=X+Y,
Not by using the build_in predictors, such as plus or is.

Thank you 

