generalized the theorem zless_zero_nat to zless_nat_eq_int_zless, and reorganized
generalized the theorem zless_zero_nat to zless_nat_eq_int_zless, and
reorganized

MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle