reserve p,q,r for FinSequence;
reserve u,v,x,y,y1,y2,z for object, A,D,X,Y for set;
reserve i,j,k,l,m,n for Nat;

theorem Th22:
  x in dom p implies x in dom(p ^ q)
proof
  dom p c= dom(p ^ q) by FINSEQ_1:26;
  hence thesis;
end;
