# Concatenation of lists

Starting from a list of lists and some extra lists, I want to combine them in various ways.

Suppose I have the following lists:

a list of lists

`A = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]`

two extra lists

`U = [100, 200, 300] V = [40, 50, 60]`

How to extend `A`

using `U`

and `V`

to obtain

```
B = [[1, 2, 3], [4, 5, 6], [7, 8, 9], [100, 200, 300]]
C = [[1, 2, 3, 100], [4, 5, 6, 200], [7, 8, 9, 300]]
D = [[1, 2, 3, 100], [4, 5, 6, 200], [7, 8, 9, 300], [40, 50, 60, a]]
```

for a given `a`

.

I have the same question with matrices and vectors.

And is there a mechanism to go back to lists from matrices and vectors?