$2\mathrm{.}5\mathrm{.}11$ Let $$ be $\{not,{?}^{{?}^{?}},EE,=\}.$ Suppose that we construct another economical version of PL

that is based on these connectives, quantifier, and the identity predicate. Let us call this

version PL $.$ Define a deduction system DS$,$ that is minimal, sound, and complete for PL $.$

Assuming that MDS is complete, prove that your deduction system is also complete by

deriving the rules of MDS from it$.$