Original sentence: Lα+1, the set {x,y} need not be an element of  Lα+1
Edited sentence: However, Lα does have the desirable property of being closed under Delta-0 Comprehension.Jensen's modified hierarchy retains this property and the slightly weaker condition that , but is also closed under pairing.Lα+1 - Lα, the set {x,y} will not be an element of  Lα+1, since it is not a subset of Lα