reserve i for Nat,
  j for Element of NAT,
  X,Y,x,y,z for set;
reserve C for initialized ConstructorSignature,
  s for SortSymbol of C,
  o for OperSymbol of C,
  c for constructor OperSymbol of C;
reserve a,b for expression of C, an_Adj C;
reserve t, t1,t2 for expression of C, a_Type C;
reserve p for FinSequence of QuasiTerms C;
reserve e for expression of C;
reserve a,a9 for expression of C, an_Adj C;
reserve q for pure expression of C, a_Type C,
  A for finite Subset of QuasiAdjs C;
reserve T for quasi-type of C;

theorem Th108:
  for t being ground pure expression of C, a_Type C
  holds ({} QuasiAdjs C) ast t is ground
proof
  let t be ground pure expression of C, a_Type C;
  set T = ({} QuasiAdjs C) ast t;
  thus variables_in T = variables_in t by Th106
    .= {} by Th107;
end;
