# `acme-zero` and `acme-one`
[Cabal][cabal] package dependencies form a commutative monoid with an absorbing
element. They satisfy the following axioms:
[cabal]: https://www.haskell.org/cabal/users-guide/developing-packages.html
* **Associativity**
For all dependencies `a`, `b` and `c`,
```
(a , b) , c = a , (b , c)
```
In fact, the Cabal syntax does not even allow you to use the parentheses for
this reason.
* **Commutativity**
For all dependencies `a` and `b`,
```
a , b = b , a
```
* **Identity element**
For all dependencies `a`,
```
acme-one , a = a , acme-one = a
```
Depending on [`acme-one`][acme-one] has no additional effect.
* **Absorbing element**
For all dependencies `a`,
```
acme-zero , a = a , acme-zero = acme-zero
```
Depending on [`acme-zero`][acme-zero] in addition has the same effect as
*only* depending on `acme-zero`.
[acme-one]: https://hackage.haskell.org/package/acme-one
[acme-zero]: https://hackage.haskell.org/package/acme-zero