= Solution
{c}
The <constructible hierarchy> is defined by <transfinite recursion> using the <definable power set>. With parameters permitted in the internal definitions, write $\operatorname{Def}(A,1)$ for the definable subsets of $A$. Then
$$
\boxed{L_0=\varnothing,\qquad L_{\alpha+1}=\operatorname{Def}(L_\alpha,1),\qquad L_\lambda=\bigcup_{\alpha<\lambda}L_\alpha\quad(\lambda\text{ a nonzero limit ordinal}).}
$$
Its class union is the <constructible universe> $L=\bigcup_{\alpha\in\operatorname{Ord}}L_\alpha$. Only subsets definable over $(L_\alpha,\in)$ using a <first-order formula> and finitely many parameters from $L_\alpha$ enter at a successor stage.
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