uncaught exception: error(existence_error(procedure,even/1),top_level/0)

[James Gale]

Hi I'm a newbee to prolog, and have just installed gnu prolog but what every
I enter into the console I get this error, uncaught exception:
error(existence_error(procedure,even/1),top_level/0)

example.

GNU Prolog 1.3.1
By Daniel Diaz
Copyright (C) 1999-2009 Daniel Diaz
| ?- even(X).
uncaught exception: error(existence_error(procedure,even/1),top_level/0)

not sure if the installation was wrong, but got not errors or I'm missing
something very simple.
also is there a good FAQ's page for this interpreter.

many thanks

James.

ps. sorry if this is a silly posting but didn't know what else to try :S 

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