Consider a certain formal system with only axiom **Excluded Middle** -$EM$ [![enter image description here][1]][1] and 18 inference rules: 9 implicative ruules (clearly not independent) [![enter image description here][2]][2] and 9 tautological rules: [![enter image description here][3]][3] If we have substitution at hands as well but we are restricted no to use conditional proof. >Is this particular system complete? I always believed that the system is complete. But once I decided to prove or disprove completeness I stuck. I neither can find any reference neither nor can proof completeness. If someone is familiar with this system I would be grateful to have some reference or proof. [1]: https://i.sstatic.net/o5WuK.png [2]: https://i.sstatic.net/6nGnu.png [3]: https://i.sstatic.net/fUZCG.png