`type t`

Type of edges.

`type label`

Type of labels on edges.

Maximum and minimum capacities for a label on an edge.

`val max_capacity : label -> t`

Current flow for a label on an edge.

`val flow : label -> t`

`+` and `-` on flows.

`val add : t -> t -> t`
`val sub : t -> t -> t`

Neutral element for `add` and `sub`.

`val zero : t`

A total ordering over flows.

`val compare : t -> t -> int`