## union

### Instructions

Write a program that takes two `string` and displays, without doubles, the characters that appear in either one of the `string`.

The display will be in the order that the characters will appear on the command line and will be followed by a newline (`'\n'`).

If the number of arguments is different from 2, then the program displays newline (`'\n'`).

### Usage

```console
student@ubuntu:~/[[ROOT]]/union$ go build
student@ubuntu:~/[[ROOT]]/union$ ./union "zpadinton" "paqefwtdjetyiytjneytjoeyjnejeyj" | cat -e
zpadintoqefwjy$
student@ubuntu:~/[[ROOT]]/union$ ./union "ddf6vewg64f" "gtwthgdwthdwfteewhrtag6h4ffdhsd" | cat -e
df6vewg4thras$
student@ubuntu:~/[[ROOT]]/union$ ./union "rien" "cette phrase ne cache rien" | cat -e
rienct phas$
student@ubuntu:~/[[ROOT]]/union$ ./union | cat -e
$
student@ubuntu:~/[[ROOT]]/union$ ./union "rien" | cat -e
$
student@ubuntu:~/[[ROOT]]/union$
```