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dekker.one
1include "subgraph.mzn";
2
3predicate fzn_tree(int: N, int: E, array[int] of int: from, array[int] of int: to,
4 var int: r, array[int] of var bool: ns, array[int] of var bool: es) =
5 let {
6 array[1..2*E] of int: dfrom = from ++ to;
7 array[1..2*E] of int: dto = to ++ from;
8 array[1..2*E] of var bool: des;
9 } in
10 /* ensure that the directed edges selected agree with undirected edges */
11 forall(e in 1..E)(es[e] <-> (des[e] \/ des[e+E])) /\
12 /* duplicate the edges so that the we can use directed graph reachability */
13 fzn_dtree(N,2*E,dfrom,dto,r,ns,des);
14
15%-----------------------------------------------------------------------------%