reserve Al for QC-alphabet;
reserve a,b,b1 for object,
  i,j,k,n for Nat,
  p,q,r,s for Element of CQC-WFF(Al),
  x,y,y1 for bound_QC-variable of Al,
  P for QC-pred_symbol of k,Al,
  l,ll for CQC-variable_list of k,Al,
  Sub,Sub1 for CQC_Substitution of Al,
  S,S1,S2 for Element of CQC-Sub-WFF(Al),
  P1,P2 for Element of QC-pred_symbols(Al);

theorem
  VERUM(Al).(x,y) = VERUM(Al)
proof
  set S = [VERUM(Al),Sbst(x,y)];
  S is Al-Sub_VERUM by SUBSTUT1:def 19;
  hence thesis by SUBLEMMA:3;
end;
