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

theorem Th10: ::FINSEQ_5:31
 p/^0 = p
proof
  per cases;
  suppose
A1: 0 <len p;
A2: now
      let i;
      assume i < len(p/^0);
      hence (p/^0).i = p.(i+(0 qua Element of NAT)) by Def2,AFINSQ_1:86
        .= p.i;
    end;
    len(p/^0) = len p - 0 by A1,Th7
      .= len p;
    hence thesis by A2,AFINSQ_1:9;
  end;
  suppose
A3: 0>=len p;
    then p/^0 ={} by Th6;
    hence thesis by A3;
  end;
end;
