title: Creating a predicate that detects if a list contains repeated elements in Prolog
body: <p>I need to define a predicate which detects if a list contains repeated elements. I cannot make use of <code>findall/3</code> or related predicates. I do not want to delete the duplicate,  I would like to figure out if there is an element that is repeated or duplicated and then have Prolog output 'yes' if there is a duplicate in a set or 'no' if there is not. I am new to Prolog and I cannot figure out how to do this without using a predicate already in Prolog. I need to come up with a new one (like redundant/1 or something of that nature). Is anybody able to help?</p>