theorem Th37:
  for P being QC-pred_symbol of k, A for l being QC-variable_list of
  k, A holds Vars(P!l,V) = variables_in(l, V) &
  Vars((P!l),V) = { l.i : 1 <= i & i
  <= len l & l.i in V }
proof
  let P be QC-pred_symbol of k, A;
  let l be QC-variable_list of k, A;
A1: P!l is atomic;
  then the_arguments_of (P!l) = l by QC_LANG1:def 23;
  hence thesis by A1,Th36;
end;
