theorem Th5: for x being set holds ::#th5 1, to be replaced by Th30
(x is non empty FinSequence of D iff x in D*\{{}})
proof
let x be set;
thus x is non empty FinSequence of D implies x in D*\{{}}
proof
assume x is non empty FinSequence of D;
then not x in {{}} & x in D* by FINSEQ_1:def 11, TARSKI:def 1;
hence thesis by XBOOLE_0:def 5;
end;
assume x in D*\{{}}; then
x in D* & not x in {{}} by XBOOLE_0:def 5;
hence thesis by FINSEQ_1:def 11, TARSKI:def 1;
end;
