Move short-hand description from math to subexpression page

Author: rgwood

book/math.md

@@ -70,23 +70,3 @@ Math operations are evaluated in the follow order (from highest precedence to lo
 > 3 * (1 + 2)
 9
 ```
-
-## Short-hand math mode
-
-A variation of math mode that Nushell supports is called "short-hand" math mode. This is because it gives you a way of accessing columns using a simple short-hand.
-
-You may have already used this functionality before. If, for example, we wanted to only see rows from `ls` where the entry is at least ten kilobytes, we can write:
-
-```
-> ls | where size > 10kb
-```
-
-The `where size > 10kb` is a command with two parts: the command name `where` and the short-hand math expression `size > 10kb`. We say short-hand because `size` here is the shortened version of writing `$it.size`.  If we look at the fully expanded form, we would see:
-
-```
-> ls | where {|$it| $it.size > 10kb }
-```
-
-Rather than having to type all this out every time a command needs to work with column data, we use this short-hand mode to access column data.
-
-For the expansion to work, the column name must appear on the left-hand side of the operation. Above, `size` appears on the left-hand side of the comparison, which allows the expression to expand into the full math mode block.

book/variables_and_subexpressions.md

@@ -63,3 +63,21 @@ We can do a very similar action in a single step using a subexpression path:
 ```
 
 It depends on the needs of the code and your particular style which form works best for you.
+
+## Short-hand subexpressions
+
+Nushell supports accessing columns in a subexpression using a simple short-hand. You may have already used this functionality before. If, for example, we wanted to only see rows from `ls` where the entry is at least ten kilobytes we can write:
+
+```
+> ls | where size > 10kb
+```
+
+The `where size > 10kb` is a command with two parts: the command name `where` and the short-hand expression `size > 10kb`. We say short-hand because `size` here is the shortened version of writing `$it.size`. This could also be written in any of the following ways:
+
+```
+> ls | where $it.size > 10kb
+> ls | where ($it.size > 10kb)
+> ls | where {|$it| $it.size > 10kb }
+```
+
+For short-hand syntax to work, the column name must appear on the left-hand side of the operation (like `size` in `size > 10kb`).