grammar fixes by Bob

Author: avehtari

src/reference-manual/expressions.qmd

@@ -783,8 +783,8 @@ In addition to single integer indexes, as described in
 Multiple indexes can be integer arrays of indexes, lower
 bounds, upper bounds, lower and upper bounds, or simply shorthand for
 all of the indexes.  If the upper bound is smaller than the lower bound, 
-the range is empty (unlike, e.g. in R). Upper bound and lower bound can be 
-expressions that evaluate to integer. A complete table of index types is 
+the range is empty (unlike, e.g., in R). The upper bound and lower bound can be 
+expressions that evaluate to integer. A complete list of index types is 
 given in the following table.
 
 ##### Indexing Options Table {- #index-types-table}