consider l being object such that
A1: l in L by XBOOLE_0:def 1;
reconsider l = l as set by TARSKI:1;
consider t being object such that
A2: t in X by XBOOLE_0:def 1;
PairSet (t,l) in PairSetFamily L by A2, A1, Def10;
hence not PairSetFamily L is empty ; :: thesis: verum