diff --git a/src/pages/learn/basics/variables.mdx b/src/pages/learn/basics/variables.mdx
index 7f222b0..9ac9178 100644
--- a/src/pages/learn/basics/variables.mdx
+++ b/src/pages/learn/basics/variables.mdx
@@ -29,6 +29,15 @@ val surname = "Doe"
 val year_of_birth = 1984
 `} />
 
+It's a compile error to attempt to modify it
+
+<Code level={2} thpcode={`
+val surname = "Doe"
+surname = "Dane"    // Error
+`} />
+
+
+
 ### Datatype annotation
 
 Written after the `val` keyword but before the variable name.
@@ -64,6 +73,8 @@ Defined with `var`, followed by a variable name and a value.
 <Code level={2} thpcode={`
 var name = "John"
 var age = 32
+
+age = 33
 `} />
 
 ### Datatype annotation
diff --git a/src/pages/learn/classes/constructor.mdx b/src/pages/learn/classes/constructor.mdx
index b727b2a..0a8c6b4 100644
--- a/src/pages/learn/classes/constructor.mdx
+++ b/src/pages/learn/classes/constructor.mdx
@@ -67,6 +67,21 @@ class Dog(String name)
 }
 `} />
 
+This would be equilavent to the following PHP code:
+
+```php
+class Dog {
+    public string $name;
+    private int $name_len;
+
+    public function __construct(string $name) {
+        $this->name = $name;
+        $this->name_len = size($name);
+        print("Dog created: $name");
+    }
+}
+```
+
 
 
 
@@ -115,41 +130,33 @@ print(a2.name_length)   //: 3
 
 ### Constructor that may fail
 
+A constructor may only fail if there is code
+that can fail on the `init` block.
+
+
+
 TBD
 
 Proposal 1:
 
-<Code thpcode={`
-class PrayingMantis(String name) -> self!Error
-`} />
-
-Proposal 2:
-
 <Code thpcode={`
 class PrayingMantis(String name)
 throws Error
-`} />
-
-Proposal 3:
-
-<Code thpcode={`
-class PrayingMantis(String name)
 {
-    init -> self!Error
+    init -> Error!
     {
-        // Something that may fail
+        // Initialization code that may fail
     }
 }
 `} />
 
 
-
 ## Destructor
 
 The destructor in THP is the same as PHP.
 
 <Code thpcode={`
-class Owl
+class Owl()
 {
     pub fun __destruct()
     {
diff --git a/src/pages/learn/classes/definition.mdx b/src/pages/learn/classes/definition.mdx
index 6c3cf0b..bfe502f 100644
--- a/src/pages/learn/classes/definition.mdx
+++ b/src/pages/learn/classes/definition.mdx
@@ -15,11 +15,13 @@ Classes in THP are significantly different than PHP.
 A class is defined as follows:
 
 <Code thpcode={`
-class Animal
+class Animal() {}
 `} />
 
 The name of the class **MUST** begin with an uppercase letter.
 
+Classes have a parameter list even if they have no parameters
+for consistency sake.
 
 
 ## Instanciation
@@ -38,7 +40,7 @@ Properties are declared with `var`/`val` inside a block.
 They **must** explicitly declare their datatype.
 
 <Code thpcode={`
-class Person
+class Person()
 {
     // This is an error. Properties must declare their datatype,
     // even if the compiler can infer it.
@@ -55,7 +57,7 @@ class Person
 **Properties are private by default**, but can be made public with `pub`.
 
 <Code thpcode={`
-class Person
+class Person()
 {
     // Properties are private by default
     val String name = "John Doe"
@@ -86,7 +88,7 @@ in the Constructor page.
 Methods are declared with `fun`, as regular functions.
 
 <Code thpcode={`
-class Person
+class Person()
 {
     fun greet()
     {
@@ -98,7 +100,7 @@ class Person
 **Methods are private by default**, and are made public with `pub`.
 
 <Code thpcode={`
-class Person
+class Person()
 {
     // This method is private
     fun private_greet()
@@ -123,7 +125,7 @@ in THP a method cannot have the same name as a property and viceversa.
 Doing so is a compile error.
 
 <Code thpcode={`
-class Person
+class Person()
 {
     String name = "Rose"
 
@@ -141,7 +143,7 @@ THP uses the dollar sign `$` as this inside classes.
 It is **required** when using a class property/method.
 
 <Code thpcode={`
-class Person
+class Person()
 {
     val String name = "Jane Doe"
 
@@ -168,7 +170,7 @@ class Animal(var String name)
 {
     pub fun set_name(String new_name)
     {
-        $name = new_name    // Error: Cannot mutate $
+        $name = new_name    // Error: Cannot mutate $name
     }
 }
 `} />
@@ -189,21 +191,3 @@ var michi = Animal("Michifu")
 michi.set_name("Garfield")
 `} />
 
-## Class constructor that may return an error
-
-Working theory:
-
-<Code thpcode={`
-class Fish(
-    val String name,
-    var Int lives = 9,
-)
-extends Animal(name)
-throws Error
-
-val fish_result = Fish("bubble")   // fish_result will be a \`Result[Fish,Error]\`
-val fish = try fish_result
-`} />
-
-
-
diff --git a/src/pages/learn/classes/inheritance.mdx b/src/pages/learn/classes/inheritance.mdx
index 2ccd484..c5fbcb2 100644
--- a/src/pages/learn/classes/inheritance.mdx
+++ b/src/pages/learn/classes/inheritance.mdx
@@ -6,7 +6,7 @@ import Code from "../../../components/Code.astro"
 
 # Inheritance
 
-
+A class inherits from another using the `extends` keyword.
 
 <Code thpcode={`
 // Base class
@@ -20,7 +20,34 @@ class Animal(var String name)
 
 // Child class
 class Cat(String name, Int lives) 
-extends Animal(name)
+extends Animal(name) {}
 
 Cat("Michi", 9).say_name()
 `} />
+
+The call to the parent constructor is done right there, after
+the parent class name.
+
+<Code thpcode={`
+class Dog(String name) 
+extends Animal(name) {}
+//            |----|
+//  This is the call to the parent constructor
+`} />
+
+You must always call super, even if the parent doesn't
+define any parameters:
+
+<Code thpcode={`
+class Parent() {}
+
+class Child()
+extends Parent() {}
+`} />
+
+
+
+
+
+
+
diff --git a/src/pages/learn/data-structures/arrays.mdx b/src/pages/learn/data-structures/arrays.mdx
index fb21e00..713df56 100644
--- a/src/pages/learn/data-structures/arrays.mdx
+++ b/src/pages/learn/data-structures/arrays.mdx
@@ -6,7 +6,10 @@ import Code from "../../../components/Code.astro"
 
 # Arrays
 
-Use square brackets as usual.
+Arrays in THP use exclusively square brackets.
+
+More importantly, Arrays and Maps are different.
+Arrays only store values of a single datatype.
 
 ## Usage
 
@@ -16,7 +19,7 @@ val apple = fruits[0]
 
 print(apple)  // apple
 
-
+// To mutate an array, you need to declare it as var
 var numbers = [0, 1, 2, 3]
 
 numbers[3] = 5
diff --git a/src/pages/learn/flow-control/conditionals.mdx b/src/pages/learn/flow-control/conditionals.mdx
index b1cdce5..9ef5199 100644
--- a/src/pages/learn/flow-control/conditionals.mdx
+++ b/src/pages/learn/flow-control/conditionals.mdx
@@ -35,6 +35,8 @@ val result = if condition { value1 } else { value2 }
 
 ## Check for datatypes
 
+TBD
+
 <Code thpcode={`
 if variable is Datatype
 {
diff --git a/src/pages/learn/functions/higher-order.mdx b/src/pages/learn/functions/higher-order.mdx
index d24276f..e5dbd9e 100644
--- a/src/pages/learn/functions/higher-order.mdx
+++ b/src/pages/learn/functions/higher-order.mdx
@@ -7,7 +7,7 @@ import Code from "../../../components/Code.astro"
 # Higher Order functions
 
 
-## Function as parameter
+## Function as parameters
 
 <Code thpcode={`
 fun map[A, B](Array[A] input, (A) -> (B) function) -> Array[B]
diff --git a/src/pages/learn/functions/lambdas.mdx b/src/pages/learn/functions/lambdas.mdx
index 2d18872..2ece501 100644
--- a/src/pages/learn/functions/lambdas.mdx
+++ b/src/pages/learn/functions/lambdas.mdx
@@ -9,18 +9,48 @@ import Code from "../../../components/Code.astro"
 
 ## Anonymous function
 
+An anonymous function is declared with `fn`.
+Other than not having a name, it can declare parameter
+and return types.
+
 <Code thpcode={`
-fun(Int x, Int y) -> Int {
+fn(Int x, Int y) -> Int {
     x + y
 }
+`} />
 
+Anonymous function can omit declaring those types as well:
 
+<Code thpcode={`
 numbers.map(fun(x) {
     x * 2
 })
 `} />
 
 
+## Anonymous function short form
+
+If you need an anonymous function that returns a single
+expression you can write it like this:
+
+<Code thpcode={`
+fun(x, y) = x + y
+`} />
+
+It uses an equal `=` instead of an arrow. It can contain
+only a single expression.
+
+This is common when declaring functions that immediately
+return a map.
+
+<Code thpcode={`
+fn(value) = .{
+    value
+}
+`} />
+
+
+
 
 ## Closure types
 
diff --git a/src/pages/learn/functions/parameters.mdx b/src/pages/learn/functions/parameters.mdx
index f5d1769..09252e2 100644
--- a/src/pages/learn/functions/parameters.mdx
+++ b/src/pages/learn/functions/parameters.mdx
@@ -41,10 +41,11 @@ Placing a `mut` before the type makes the parameter a mutable
 reference. Mutable methods can be used, and the original
 data **can** be mutated.
 
-The caller *must* also use `mut`.
+The caller must define the value as `var`, and when calling
+must use `mut`.
 
 <Code thpcode={`
-val numbers = Array(0, 1, 2, 3)
+var numbers = Array(0, 1, 2, 3)
 
 push_25(mut numbers)    // Pass \`numbers\` as reference.
 
@@ -64,6 +65,8 @@ fun add_25(clone Array[Int] numbers) {
 Using the `clone` keyword before the type creates a mutable copy
 of the parameter (CoW). The original data will **not** be mutated.
 
+The caller must also use `clone` when calling the function.
+
 
 <Code thpcode={`
 val numbers = Array(1, 2, 3, 4)