diff --git a/progress.md b/progress.md
index 341b75e..2022c37 100644
--- a/progress.md
+++ b/progress.md
@@ -57,9 +57,9 @@
  - [x] 7.4 Parsing Flags with flag.Value
  - [x] 7.5 Interface Values
  - [x] 7.6 Sorting with sort.Interface
- - [ ] 7.7 The http.Handler Interface
- - [ ] 7.8 The error Interface
- - [ ] 7.9 Example: Expression Evaluator
+ - [x] 7.7 The http.Handler Interface
+ - [x] 7.8 The error Interface
+ - [x] 7.9 Example: Expression Evaluator
  - [ ] 7.10 Type Assertions
  - [ ] 7.11 Discriminating Errors with Type Assertions
  - [ ] 7.12 Querying Behaviors with Interface Type Assertions
@@ -79,7 +79,7 @@
  - [x] 8.10 Example: Chat Server
 - [x] Chapter 9: Concurrency with Shared Variables
  - [x] 9.1 Race Conditions
- - [ ] 9.2 Mutual Exclusion: sync.Mutex
+ - [x] 9.2 Mutual Exclusion: sync.Mutex
  - [x] 9.3 Read/Write Mutexes: sync.RWMutex
  - [x] 9.4 Memory Synchronization
  - [x] 9.5 Lazy Initialization: sync.Once
@@ -117,4 +117,3 @@
  - [x] 13.3 Example: Deep Equivalence
  - [x] 13.4 Calling C Code with cgo
  - [x] 13.5 Another Word of Caution
-