reserve X for ComplexUnitarySpace;
reserve g for Point of X;
reserve seq, seq1, seq2 for sequence of X;
reserve Rseq for Real_Sequence;
reserve Cseq,Cseq1,Cseq2 for Complex_Sequence;
reserve z,z1,z2 for Complex;
reserve r for Real;
reserve k,n,m for Nat;

theorem
  seq.1 = Sum(seq,1) - Sum(seq,0)
proof
  seq.(0+1) = Sum(seq,0+1) - Sum(seq,0) by Th19;
  hence thesis;
end;
