diff --git a/subjects/nextprime/README.md b/subjects/nextprime/README.md
index 5c1ef2fc..138c7a14 100644
--- a/subjects/nextprime/README.md
+++ b/subjects/nextprime/README.md
@@ -2,7 +2,7 @@
 
 ### Instructions
 
-Write a function that returns the first prime number that is equal or superior to the `int` passed as parameter.
+Write a **function** which returns the first prime number which is equal or superior to the `u64` passed as parameter.
 
 The function must be optimized in order to avoid time-outs with the tester.
 
diff --git a/subjects/order_books/README.md b/subjects/order_books/README.md
index e527a399..2e50f0d1 100644
--- a/subjects/order_books/README.md
+++ b/subjects/order_books/README.md
@@ -2,29 +2,31 @@
 
 ### Instructions
 
-Build a module called `library` with two sub-modules inside it:
+Build a module called `library` with two sub-modules inside of it:
 
-- `writers` which contains a structure called `Writer` that has a first_name (String), last_name (String) and a set of books (Vec\<Book\>).
-- `books` which contains a structure called `Book` that has a title (String) and a year of publish (u64).
+- `writers` which contains a structure called `Writer` which has a first_name (String),a last_name (String) and a set of books (Vec\<Book\>).
+- `books` which contains a structure called `Book` which has a title (String) and a year of publication (u64).
 
-You will also have to create (outside the previous modules) a function `order_books` that receives a writer (Writer) and orders the set of books alphabetically.
+A function `order_books` also has to be created (outside the previous modules which receives a writer (Writer) and orders the set of books alphabetically.
 
 ### Expected Functions and Structs
 
+#### (The structs declarations need to be filled and added in the appropriate submodules)
+
 ```rs
-pub fn order_books(writer: &mut Writer) {
+pub struct Writer {
 
 }
 ```
 
 ```rs
-struct Writer {
+pub struct Book {
 
 }
 ```
 
 ```rs
-struct Book {
+pub fn order_books(writer: &mut Writer) {
 
 }
 ```
@@ -34,6 +36,9 @@ struct Book {
 Here is a program to test your function and structs:
 
 ```rs
+pub use library::writers::Writer;
+pub use library::books::Book;
+
 fn main() {
     let mut writer_a = Writer {
         first_name: "William".to_string(),
diff --git a/subjects/previousprime/README.md b/subjects/previousprime/README.md
index 44ddbd0d..cc377602 100644
--- a/subjects/previousprime/README.md
+++ b/subjects/previousprime/README.md
@@ -2,9 +2,9 @@
 
 ### Instructions
 
-Write a function that returns the first prime number that is equal or inferior to the `int` passed as parameter.
+Write a **function** which returns the first prime number which is equal or inferior to the `u64` passed as parameter.
 
-If there are no primes inferior to the `int` passed as parameter the function should return 0.
+If there are no primes inferior to the `u64` passed as parameter the function should return `0`.
 
 ### Expected function
 
diff --git a/subjects/rot21/README.md b/subjects/rot21/README.md
index aa20978f..06b91465 100644
--- a/subjects/rot21/README.md
+++ b/subjects/rot21/README.md
@@ -2,17 +2,19 @@
 
 ### Instructions
 
-Your purpose in this exercise is to create a `rot21` function that works like the ROT13 cipher.
+The purpose of this exercise is to create a `rot21` function that works like the ROT13 cipher.
 
-Your function will receive a string and it will rotate each letter of that string 21 times to the right.
+This function will receive a `string` and it will rotate each letter of that `string` 21 times to the right.
 
-Your function should only change letters. If the string includes punctuation, symbols and numbers
+The function should only rotate letters. If the string includes punctuation, symbols and/or numbers
 they will remain the same.
 
 ### Expected functions
 
 ```rust
-pub fn rot21(input: &str) -> String {}
+pub fn rot21(input: &str) -> String {
+
+}
 ```
 
 ### Usage
@@ -32,7 +34,7 @@ fn main() {
 
 ```
 
-And its output
+And its output:
 
 ```console
 student@ubuntu:~/[[ROOT]]/test$ cargo run