reserve i,k for Nat;
reserve A for QC-alphabet;
reserve x for bound_QC-variable of A;
reserve a for free_QC-variable of A;
reserve p,q for Element of QC-WFF(A);
reserve l for FinSequence of QC-variables(A);
reserve P,Q for QC-pred_symbol of A;
reserve V for non empty Subset of QC-variables(A);
reserve s,t for QC-symbol of A;

theorem Th36:
  p is atomic implies Vars(p,V) = variables_in(the_arguments_of p,
V) & Vars(p,V) = { (the_arguments_of p).k : 1 <= k & k <= len (the_arguments_of
  p) & (the_arguments_of p).k in V }
proof
  assume p is atomic;
  hence Vars(p,V) = variables_in(the_arguments_of p, V) by Lm2;
  hence thesis;
end;
