reserve f for Function;
reserve n,k,n1 for Nat;
reserve r,p for Real;
reserve x,y,z for object;
reserve seq,seq1,seq2,seq3,seq9,seq19 for Real_Sequence;

theorem
  seq1-(seq2+seq3)=seq1-seq2-seq3
proof
  thus seq1-(seq2+seq3)=seq1+(-seq2+(-1)(#)seq3) by Th22
    .=seq1-seq2-seq3 by Th13;
end;
