reserve A for preIfWhileAlgebra,
  C,I,J for Element of A;
reserve S for non empty set,
  T for Subset of S,
  s for Element of S;

theorem Th50:
  for A being preIfWhileAlgebra
  for I1,I2 being Element of A st I1 <> I1\;I2 & I2 <> I1\;I2
  holds I1\;I2 nin ElementaryInstructions A
proof
  let A be preIfWhileAlgebra;
  let I1,I2 be Element of A;
  assume that
A1: I1 <> I1\;I2 and
A2: I2 <> I1\;I2;
  I1\;I2 in {J1 \; J2 where J1,J2 is Algorithm of A:
  J1 <> J1\;J2 & J2 <> J1\;J2} by A1,A2;
  hence thesis by XBOOLE_0:def 5;
end;
