findall with @< fails on when there is only one answer

Hello, 

I use this in a predicate :

  findall(Person - Y, (siblings(Person,Y), Person @< Y)  Sibs).

This one gives a empty list if the person is futher on the alfabeth then Y.

If I delete it , it gives the right answers.
Also if there is more then 1 answers , it gives the right answer.

Is it right that sorting (@<) is not working when there is only 1 answer.
and if so, can I then better sort when there are more then 1 answer. 

Roelof



 		 	   		  
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