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dekker.one
1predicate fzn_dag(array[int] of $$N: from, array[int] of $$N: to,
2 array[$$N] of var bool: ns, array[int] of var bool: es) =
3 let {
4 set of int: EDGE = index_set(es);
5 array[index_set(ns)] of var 0..length(ns)-1: dist; /* distance of longest path */
6
7 } in
8 forall(n in index_set(ns))(not ns[n] -> dist[n] = 0) /\
9 forall(e in EDGE)
10 (es[e] -> dist[from[e]] + 1 <= dist[to[e]])
11 /\
12 % redundant constraint to ensure all distances are fixed
13 forall(n in index_set(ns))
14 (dist[n] = max( [0] ++ [ (dist[from[e]] + 1)*es[e] | e in EDGE where to[e] = n ]))
15 ;