clear screens and list membership

From: JNY (jny0_at_hotmail.com)
Date: 01/05/04 

Date: 5 Jan 2004 02:40:39 -0800

I am using swi-prolog, and have two problems:

I need to clear a screen. I have been using the following:

cls:- put(27),put(91),put(56),put(74).

It doesn't seem to work for me, despite being assured that it works.

The second problem I have, is that I need to test for whether a list
is empty. I would like it to work something like this:

is_empty(list) /*succeeds if empty, fails if not*/

Any ideas would be gratefully received.
Cheers
JNY