Removed NF -> N

Exercise3.md

@@ -102,7 +102,6 @@ Here:
   - For array indexes (`i` in `a[i]`), print `NI`.
   - For arrays that we are indexing in an array indexing expression (`a` in `a[i]`), print `NA`.
   - For the base object in a field access (`o` in`o.x`), print `NO`.
-  - For writes to `nonnull` fields, print `NF`.
    - Otherwise (parameters, returns, local/global variable assignments), print `N`
 
 You may print other lines (e.g. for debugging), as long as they do not start with `N`.
@@ -133,12 +132,12 @@ fun main(n : int) = {
 Your analysis should print the following:
 
 ```
-NF 6 29 -> obj 6 29
-NF 8 4 -> null 3 50
+N 6 29 -> obj 6 29
+N 8 4 -> null 3 50
 ```
 
 Where:
-- `NF` means that we are talking about an assignment to a nonnull field
+- `N` means that we are talking about an assignment to a nonnull variable (here, a field).
 - `6 29` refers to the source location that Teal associates with the initial field assignment
 - `obj 6 29` refers to the literal number `5`
 - `8 4` is the source location of the second assignment

examples/pair.expected

-NF 6 29 -> obj 6 29
-NF 8 4 -> null 3 50
+N 6 29 -> obj 6 29
+N 8 4 -> null 3 50

examples/simple-struct.expected

-NF 4 25 -> obj 4 25
-NF 4 28 -> obj 4 28
-NF 5 15 -> obj 5 15
-NF 5 18 -> obj 5 18
+N 4 25 -> obj 4 25
+N 4 28 -> obj 4 28
+N 5 15 -> obj 5 15
+N 5 18 -> obj 5 18
 N 8 6 -> obj 4 17
 N 8 6 -> obj 5 7
 N 8 6 -> null 4 31
\ No newline at end of file