using only the numbers 1, 2, 3 and 4, how do i get the answers -1 to -20

1-2=-1

1-3=-2

1-4=-3

1-2-3=-4

like wise........

Can you use each digit only once, or can you use some of the digits more than once?

Must you use each digit?

Can you use addition, subtraction, multiplication, division, exponentiation, finding roots, factorials, and including negative signs?

In summary, what are all the rules?