#### Exercise 1¶

Write a function `add`

that receives two numbers and returns the sum of them:

In [ ]:

```
def add(x, y):
# your code here
pass
```

In [ ]:

```
# Tests:
assert add(2, 3) == 5
assert add(4, 3) == 7
```

In [1]:

```
def add(x, y):
return x + y
```

Markdown cells can also be solutions, for example:

#### Exercise 2¶

Use LaTeX math notation, to write out the formula of *"sum of squares"*:

$$\sum_{i=1}^n i^2$$