reserve Al for QC-alphabet;
reserve a,b,c,d for object,
  i,k,n for Nat,
  p,q for Element of CQC-WFF(Al),
  x,y,y1 for bound_QC-variable of Al,
  A for non empty set,
  J for interpretation of Al,A,
  v,w for Element of Valuations_in(Al,A),
  f,g for Function,
  P,P9 for QC-pred_symbol of k,Al,
  ll,ll9 for CQC-variable_list of k,Al,
  l1 for FinSequence of QC-variables(Al),
  Sub,Sub9,Sub1 for CQC_Substitution of Al,
  S,S9,S1,S2 for Element of CQC-Sub-WFF(Al),
  s for QC-symbol of Al;
reserve vS,vS1,vS2 for Val_Sub of A,Al;
reserve B for Element of [:QC-Sub-WFF(Al),bound_QC-variables(Al):],
  SQ for second_Q_comp of B;
reserve B for CQC-WFF-like Element of [:QC-Sub-WFF(Al),
  bound_QC-variables(Al):],
  xSQ for second_Q_comp of [S,x],
  SQ for second_Q_comp of B;
reserve B1 for Element of [:QC-Sub-WFF(Al),bound_QC-variables(Al):];
reserve SQ1 for second_Q_comp of B1;
reserve a for Element of A;

theorem Th75:
  for v,vS,vS1,vS2 st (for y st y in dom vS1 holds not y in
still_not-bound_in (P!ll)) & (for y st y in dom vS2 holds vS2.y = v.y) & dom vS
  misses dom vS2 holds J,v.vS |= P!ll iff J,v.(vS+*vS1+*vS2) |= P!ll
proof
  let v,vS,vS1,vS2 such that
A1: for y st y in dom vS1 holds not y in still_not-bound_in (P!ll) and
A2: ( for y st y in dom vS2 holds vS2.y = v.y)& dom vS misses dom vS2;
A3: for y st y in dom vS1 holds not y in still_not-bound_in ll
  proof
    let y;
    assume y in dom vS1;
    then not y in still_not-bound_in (P!ll) by A1;
    hence thesis by QC_LANG3:5;
  end;
A4: (v.(vS+*vS1+*vS2))*'ll in J.P iff Valid(P!ll,J).(v.(vS+*vS1+*vS2)) =
  TRUE by VALUAT_1:7;
  Valid(P!ll,J).(v.vS) = TRUE iff (v.vS)*'ll in J.P by VALUAT_1:7;
  hence thesis by A2,A3,A4,Th74,VALUAT_1:def 7;
end;
