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_8:9
  mid(p^q,len p+1,len p+len q)=q
proof
A1: (len p +1)-'1=len p by NAT_D:34;
  len (p^q)=len p + len q by AFINSQ_1:17;
  hence thesis by A1,Th12;
end;
