seed 1: first failure at trial 46509 (n=19, k=4): a cycle of Delta has non-positive length at vertex 12
arcs [(0, 5), (0, 8), (0, 10), (0, 11), (0, 17), (1, 5), (1, 6), (1, 8), (1, 10), (1, 11), (1, 18), (2, 4), (2, 12), (3, 4), (3, 8), (3, 14), (3, 16), (4, 5), (4, 6), (4, 7), (4, 8), (4, 9), (4, 10), (5, 6), (5, 7), (6, 9), (8, 9), (8, 10), (8, 11), (8, 12), (8, 14), (8, 15), (10, 11), (10, 12), (10, 14), (10, 15), (11, 12), (11, 13), (11, 16), (12, 13), (12, 14), (12, 15), (12, 16), (12, 17), (14, 16), (14, 17), (16, 17), (16, 18), (17, 18)]
roots [0, 1, 2, 3] sets [[0, 5, 6, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18], [1, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18], [2, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17], [3, 4, 8, 10, 11, 12, 14, 16, 17, 18]]
failing vertex 12 ; J(v) = [0, 1, 2, 3] ; tails of the minimum-cost assignment {0: 10, 1: 11, 2: 2, 3: 8}
   arc of Delta 0 -> 1, length -107573/6000002
   arc of Delta 0 -> 2, length -139029/3000001
   arc of Delta 0 -> 3, length -701334/3000001
   arc of Delta 1 -> 0, length 107573/6000002
   arc of Delta 1 -> 2, length 2430923/24000008
   arc of Delta 1 -> 3, length -3066267/12000004
   arc of Delta 3 -> 0, length 1249227/3000001
   arc of Delta 3 -> 1, length 2530990/3000001
   arc of Delta 3 -> 2, length 1938421/3000001
   cycle (0, 1) has length 0   <-- exactly 0: a tie
   cycle (0, 3) has length 547893/3000001
   cycle (1, 3) has length 7057693/12000004
   cycle (0, 1, 3) has length 1715495/12000004
   cycle (0, 3, 1) has length 3766885/6000002
   admissible assignment with tails [8, 10, 2, 11] has cost 262486980909/1500000500000
   admissible assignment with tails [8, 11, 2, 10] has cost 321996605909/1500000500000
   admissible assignment with tails [10, 8, 2, 11] has cost 930261730909/1500000500000
   admissible assignment with tails [10, 11, 2, 8] has cost 48050105909/1500000500000
   admissible assignment with tails [11, 8, 2, 10] has cost 989771355909/1500000500000
   admissible assignment with tails [11, 10, 2, 8] has cost 48050105909/1500000500000
   f(2) = {2: '418409/500000'}
   f(8) = {0: '-882829/3000001', 1: '398934/3000001', 2: '-193635/3000001', 3: '-2132056/3000001'}
   f(10) = {0: '-390555/12000004', 1: '-605701/12000004', 2: '-946671/12000004', 3: '-3195891/12000004'}
   f(11) = {0: '-1046987/24000008', 1: '-1477279/24000008', 2: '238411/6000002', 3: '-7609813/24000008'}
same instance, same (old) code, 50 other seeds: construction succeeded and was verified in 50 cases
