thunk with a \emph{black hole} (see Black Holes, below). When
evaluation of the thunk completes, the update frame will cause the
thunk to be overwritten again with an \emph{indirection} to the result
-of the thunk, which is always a constructor.
+of the thunk, which is always a constructor or a partial application.
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-Indirections needn't always point to a constructor. They can point to
-a chain of indirections which point to an evaluated closure. When
-revertible black holes are added, they may also point to reverted
+Indirections needn't always point to a closure in WHNF. They can
+point to a chain of indirections which point to an evaluated closure.
+When revertible black holes are added, they may also point to reverted
black holes.
\item[Thread State Objects (@TSO@s)] represent Haskell threads. Their