reserve i,j,k,n,m for Nat,
  x,y,z,y1,y2 for object, X,Y,D for set,
  p,q for XFinSequence;
reserve k1,k2 for Nat;

theorem :: FINSEQ_8:8
  mid(p,0,k)=mid(p,1,k)
proof
A1: 0-'1=0 by NAT_2:8;
  mid(p,1,k) = (p|k) by Th16;
  hence thesis by A1,Th10;
end;
