reserve Al for QC-alphabet;
reserve a,b,c,d for object,
  i,j,k,m,n for Nat,
  p,q,r for Element of CQC-WFF(Al),
  x,y,y0 for bound_QC-variable of Al,
  X for Subset of CQC-WFF(Al),
  A for non empty set,
  J for interpretation of Al,A,
  v,w for Element of Valuations_in(Al,A),
  Sub for CQC_Substitution of Al,
  f,f1,g,h,h1 for FinSequence of CQC-WFF(Al);
reserve fin,fin1 for FinSequence;

theorem Th10:
  1 <= len (fin^<*b*>) & len (fin^<*b*>) in dom (fin^<*b*>)
proof
  len (fin^<*b*>) = len fin + 1 by FINSEQ_2:16;
  then 1 <= len (fin^<*b*>) by NAT_1:11;
  hence thesis by FINSEQ_3:25;
end;
