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 Th14:
  k1>k2 implies mid(p,k1,k2) = {}
proof
  set k21=k2;
A1: len (p|k21)<=k21 by AFINSQ_1:55;
  assume
A2: k1>k2;
  then k1>= (0 qua Nat) +1 by NAT_1:13;
  then
A3: k1-'1=k1-1 by XREAL_1:233;
  k1>=k2+1 by A2,NAT_1:13;
  then k1-1>=k2+1-1 by XREAL_1:9;
  hence thesis by A3,A1,Th6,XXREAL_0:2;
end;
