reserve a,b,c,d,x,y,w,z,x1,x2,x3,x4 , X for set;
reserve A for non empty set;
reserve i,j,k for Element of NAT;
reserve a,b,c,d for Real;
reserve y,r,s,x,t,w for Element of RAT+;
reserve z,z1,z2,z3,z4 for Quaternion;
 reserve x for Real;

theorem
  Rea (z*') = Rea z & Im1 (z*') = -Im1 z &
  Im2 (z*') = -Im2 z & Im3 (z*') = -Im3 z
proof
  z*' = [*Rea z, -Im1 z, -Im2 z, -Im3 z*] by Lm19;
  hence thesis by Th16;
end;
