A two$-$stack npda is an npda with two independent stacks.$$ To define such an automaton, we modify Definition $7\mathrm{.}1$ so that$$ : Q x $(\{$$\})$ x$$ x$$finite subsets of Q x $*$ x$*.$ A move depends on the tops of the two stacks and results in new values being pushed on these two stacks.$$ Show that two$-$stack npdas are equivalent to standard Turing machines.