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An example of an LSP violation is a situation where a descendant **breaks the expectations** set by the base class. One of the most well-known examples is the *rectangle and square* relationship.

### Example:

Base class:

```python
class Rectangle:
    def __init__(self, width, height):
        self.width = width
        self.height = height

def set_width(self, w):
        self.width = w

def set_height(self, h):
        self.height = h

def area(self):
        return self.width * self.height
```

Subclass:

```python
class Square(Rectangle):
    def set_width(self, w):
        self.width = w
        self.height = w  # breaks the contract

def set_height(self, h):
        self.width = h
        self.height = h  # breaks the contract
```

### Why this is an LSP violation:

1. **The subclass changes the meaning of the methods' behavior.**
In `Rectangle`, `set_width()` changes only the width.
In `Square`, it changes the width *and the height*.
Client code does not expect this kind of behavior.
2. **Client code starts working incorrectly.**

For example:

```python
def resize(rect: Rectangle):
    rect.set_width(10)
    rect.set_height(20)
    return rect.area()
```

Expected behavior for a rectangle:

```javascript
area = 10 * 20 = 200
```

Actual behavior for a square:

```javascript
set_width(10) → width=10, height=10
set_height(20) → width=20, height=20
area = 20 * 20 = 400  # incorrect relative to expectations
```

3. **The subclass forces the client to perform type checks.**

```python
if isinstance(rect, Square):
    ...
```

This is direct proof of an LSP violation.

### Summary

`Square` **cannot substitute for** `Rectangle`, even though it formally inherits from it - and this is a classic violation of the Liskov Substitution Principle.

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