 reserve L for Quasi-Boolean_Algebra,
         x, y, z for Element of L;
 reserve L for Nelson_Algebra,
         a, b, c, d, x, y, z for Element of L;

theorem Th16:
  x < y implies a "/\" (a => x) < y
  proof
    assume
A1: x < y;
A2: a "/\" (a => x) = a "/\" ((-a) "\/" x) by Th14;
A3: a "/\" ((-a) "\/" x) = (a "/\" (-a)) "\/" (a "/\" x)
      by LATTICES:def 11;
A4: (a "/\" x) < x by Th6;
    (a "/\" (-a)) < x by Def13; then
    a "/\" (a => x) < x by A3,A2,A4,Def7;
    hence thesis by A1,Def3;
  end;
