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From: nabiel@erix.UUCP (Nabiel Elshiewy)
Newsgroups: net.lang.prolog
Subject: Re: Standard behavior?
Message-ID: <1135@erix.UUCP>
Date: Wed, 14-May-86 12:19:42 EDT
Article-I.D.: erix.1135
Posted: Wed May 14 12:19:42 1986
Date-Received: Sun, 18-May-86 14:55:28 EDT
References: <6500005@uicsl>
Reply-To: nabiel@erix.UUCP (Nabiel Elshiewy)
Organization: L M Ericsson, Stockholm, Sweden
Lines: 15

In article <6500005@uicsl> Mark Gooley (gooley@uicsl.UUCP) writes:
>
>Consider the following trivial predicate:
>
>a([]).
>a(_).
>
>Given the query :-a([]). , C-Prolog finds one match and UNSW Prolog finds two.
>Which is standard behavior?  How do other implementations behave?
>

Intuitively C-Prolog's  one  match is the  expected standard behaviour. The
two assertions describe a choice; it is either an empty  list or  something
else which differs from an empty list.
Aside: Also both Quintus Prolog and Mu-Prolog find one match.