minor fixes to text of challenge 6.9

book.tex

@@ -13206,10 +13206,10 @@ However, we limit tuples to a length of $50$ so that their length and
 pointer mask can fit into the 64-bit tag at the beginning of each
 tuple (Section~\ref{sec:data-rep-gc}). We intend arrays to allow
 millions of elements, so we need more bits to store the length.
-However, because arrays are homogeneous, we only need $1$ bit for the
-pointer mask instead of one bit per array elements.  Finally, the
-garbage collector will need to be able to distinguish between tuples
-and arrays, so we need to reserve $1$ bit for that purpose.  So we
+However, because arrays are homogeneous, we only need one bit for the
+pointer mask instead of one bit per array element.  Finally, the
+garbage collector must be able to distinguish between tuples
+and arrays, so we need to reserve one bit for that purpose.  We
 arrive at the following layout for the 64-bit tag at the beginning of
 an array:
 \begin{itemize}
@@ -13311,8 +13311,9 @@ operations. In particular, the new AST node \ALLOCARRAY{\Exp}{\Type}
 is analogous to the \code{Allocate} AST node for tuples.  The $\Type$
 argument must be \ARRAYTY{T} where $T$ is the element type for the
 array. The \code{AllocateArray} AST node allocates an array of the
-length specified by the $\Exp$ but does not initialize the elements of
-the array. Generate code in this pass to initialize the elements.
+length specified by the $\Exp$ (of type \INTTY), but does not initialize the elements of
+the array. Generate code in this pass to initialize the elements
+analogous to the case for tuples.
 
 \subsection{Remove Complex Operands}