Singular

LIB "arr.lib";
ring R = 0,(x,y,z,t),dp;
arr A = arrBraid(4);
arrposet P = arrLattice(A);
==> 
==> 
==> === Computing poset ===
==> 
==> 
==> rank 2: found 7 flats in 0s
==> rank 3: found 1 flats in 0s
==> 
==> 
==> Matrix tests: 38
P;
==> Given Arrangement:
==> _[1]=x-y
==> _[2]=x-z
==> _[3]=x-t
==> _[4]=y-z
==> _[5]=y-t
==> _[6]=z-t
==> 
==> Corresponding poset:
==> ====== rank 1: 6 flats ======
==>  (1),  (2),  (3),  (4),  (5),  (6), 
==> ====== rank 2: 7 flats ======
==>  (1,2,4),  (1,3,5),  (1,6),  (2,3,6),  (2,5),  (3,4),  (4,5,6), 
==> ====== rank 3: 1 flats ======
==>  (1,2,3,4,5,6), 
==> ====== rank 4: 0 flats ======
==> 
==> 
//As you can see the values are not calculated yet:
printMoebius(P);
==> Moebius values: 
==> ====== rank 1: 6 flats ======
==>  (-1),  (-1),  (-1),  (-1),  (-1),  (-1), 
==> ====== rank 2: 7 flats ======
==>  (0),  (0),  (0),  (0),  (0),  (0),  (0), 
==> ====== rank 3: 1 flats ======
==>  (0), 
==> ====== rank 4: 0 flats ======
==> 
P = moebius(P);
//Now all entries are initialized:
printMoebius(P);
==> Moebius values: 
==> ====== rank 1: 6 flats ======
==>  (-1),  (-1),  (-1),  (-1),  (-1),  (-1), 
==> ====== rank 2: 7 flats ======
==>  (2),  (2),  (1),  (2),  (1),  (1),  (2), 
==> ====== rank 3: 1 flats ======
==>  (-6), 
==> ====== rank 4: 0 flats ======
==>