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<H2><A NAME="sec:2.1"><SPAN class="sec-nr">2.1</SPAN> <SPAN class="sec-title">Getting 
started quickly</SPAN></A></H2>

<A NAME="sec:quickstart"></A>

<H3><A NAME="sec:2.1.1"><SPAN class="sec-nr">2.1.1</SPAN> <SPAN class="sec-title">Starting 
SWI-Prolog</SPAN></A></H3>

<A NAME="sec:startpl"></A>

<H4><A NAME="sec:2.1.1.1"><SPAN class="sec-nr">2.1.1.1</SPAN> <SPAN class="sec-title">Starting 
SWI-Prolog on Unix</SPAN></A></H4>

<A NAME="sec:startunix"></A>

<P>By default, SWI-Prolog is installed as `pl', though some 
administrators call it `swipl' or `swi-prolog'. The command-line 
arguments of SWI-Prolog itself and its utility programs are documented 
using standard Unix <B>man</B> pages. SWI-Prolog is normally operated as 
an interactive application simply by starting the program:

<PRE class="code">
machine% pl
Welcome to SWI-Prolog (Version 5.6.42)
Copyright (c) 1990-2007 University of Amsterdam.
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to redistribute it under certain conditions.
Please visit http://www.swi-prolog.org for details.

For help, use ?- help(Topic). or ?- apropos(Word).

1 ?- 
</PRE>

<P>After starting Prolog, one normally loads a program into it using
<A NAME="idx:consult1:55"></A><A class="pred" href="consulting.html#consult/1">consult/1</A>, 
which --- for historical reasons --- may be abbreviated by putting the 
name of the program file between square brackets. The following goal 
loads the file <CODE>likes.pl</CODE> containing clauses for the 
predicates likes/2 :

<PRE class="code">
?- [likes].
% likes compiled, 0.00 sec, 596 bytes.

Yes
?- 
</PRE>

<P>After this point, Unix and Windows users unite, so if you are using 
Unix please continue at <A class="sec" href="quickstart.html">section 
2.1.2</A>.

<H4><A NAME="sec:2.1.1.2"><SPAN class="sec-nr">2.1.1.2</SPAN> <SPAN class="sec-title">Starting 
SWI-Prolog on Windows</SPAN></A></H4>

<P>After SWI-Prolog has been installed on a Windows system, the 
following important new things are available to the user:

<P>
<UL>
<LI>A folder (called <EM>directory</EM> in the remainder of this 
document) called <CODE>pl</CODE> containing the executables, libraries, 
etc. of the system. No files are installed outside this directory.
<LI>A program <B>plwin.exe</B>, providing a window for interaction with 
Prolog. The program <B>plcon.exe</B> is a version of SWI-Prolog that 
runs in a DOS-box.
<LI>The file-extension <CODE>.pl</CODE> is associated with the program
<B>plwin.exe</B>. Opening a <CODE>.pl</CODE> file will cause
<B>plwin.exe</B> to start, change directory to the directory in which 
the file-to-open resides and load this file.
</UL>

<P>The normal way to start with the <CODE>likes.pl</CODE> file mentioned 
in
<A class="sec" href="quickstart.html">section 2.1.1.1</A> is by simply 
double-clicking this file in the Windows explorer.

<H3><A NAME="sec:2.1.2"><SPAN class="sec-nr">2.1.2</SPAN> <SPAN class="sec-title">Executing 
a query</SPAN></A></H3>

<A NAME="sec:execquery"></A>

<P>After loading a program, one can ask Prolog queries about the 
program. The query below asks Prolog what food `sam' likes. The system 
responds with <TT>X = &lt;<VAR>value</VAR>&gt;</TT> if it can prove the 
goal for a certain
<VAR>X</VAR>. The user can type the semi-colon (;)<SUP class="fn">3<SPAN class="fn-text">On 
most installations, single-character commands are executed without 
waiting for the <font size=-1>RETURN</font> key.</SPAN></SUP> if (s)he 
wants another solution, or <font size=-1>RETURN</font> if (s)he is 
satisfied, after which Prolog will say <B>Yes</B>. If Prolog answers <B>No</B>, 
it indicates it cannot find any (more) answers to the query. Finally, 
Prolog can answer using an error message to indicate the query or 
program contains an error.

<PRE class="code">
?- likes(sam, X).

X = dahl ;

X = tandoori ;

...

X = chips ;

No
?-
</PRE>

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