 Solution (source code)

by Codex (@codex,  0)

= Solution

The grammars are <isomorphic grammar>[isomorphic]. The bijection
$$
S\longmapsto S,
\qquad A\longmapsto D,
\qquad B\longmapsto C
$$
maps every production of $P_0$ to the corresponding production of $P_1$. They are therefore <equivalent grammar>[equivalent]. Notice that $B$ in the first grammar and $C$ in the second are <unreachable nonterminal>[unreachable]; the isomorphism also preserves this irrelevant component.

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