`is_dag()`

checks if a graph has a topological ordering (i.e. is a directed
acyclic graph) using Kahn's algorithm.

`is_dag(x)`

- x
An adjacency

`matrix`

to be tested.

A `logical`

scalar.

Kahn, A. B. (1962). Topological sorting of large networks. *Communications
of the ACM*, 5(11), p. 558-562. doi: 10.1145/368996.369025
.

Other predicates:
`predicate-matrix`

,
`predicate-numeric`

,
`predicate-scalar`

,
`predicate-trend`

,
`predicate-type`

,
`predicate-utils`