Here are a couple similar graphs that go fine:

G = {0: {1: None, 6: None, 7: None, 10: None, 11: None, 12: None, 13:
None}, 1: {0: None, 6: None, 7: None, 10: None, 11: None, 12: None,
13: None, 18: None}, 2: {3: None, 4: None, 5: None, 8: None, 9: None,
14: None, 15: None, 20: None}, 3: {2: None, 4: None, 5: None, 8: None,
9: None, 14: None, 15: None, 22: None}, 4: {2: None, 3: None, 5: None,
8: None, 9: None, 14: None, 15: None, 24: None}, 5: {2: None, 3: None,
4: None, 8: None, 9: None, 14: None, 15: None, 26: None}, 6: {0: None,
1: None, 7: None, 10: None, 11: None, 12: None, 13: None, 28: None},
7: {0: None, 1: None, 6: None, 10: None, 11: None, 12: None, 13: None,
30: None}, 8: {32: None, 2: None, 3: None, 4: None, 5: None, 9: None,
14: None, 15: None}, 9: {2: None, 3: None, 4: None, 5: None, 8: None,
34: None, 14: None, 15: None}, 10: {0: None, 1: None, 36: None, 6:
None, 7: None, 11: None, 12: None, 13: None}, 11: {0: None, 1: None,
38: None, 6: None, 7: None, 10: None, 12: None, 13: None}, 12: {0:
None, 1: None, 6: None, 7: None, 40: None, 10: None, 11: None, 13:
None}, 13: {0: None, 1: None, 6: None, 7: None, 10: None, 11: None,
12: None, 42: None}, 14: {2: None, 3: None, 4: None, 5: None, 8: None,
9: None, 44: None, 15: None}, 15: {2: None, 3: None, 4: None, 5: None,
8: None, 9: None, 14: None, 46: None}, 16: {32: None, 34: None, 44:
None, 48: None, 20: None, 22: None, 24: None, 26: None}, 17: {33:
None, 35: None, 45: None, 49: None, 21: None, 23: None, 25: None, 27:
None}, 18: {32: None, 1: None, 34: None, 46: None, 50: None, 20: None,
22: None, 24: None, 26: None}, 19: {33: None, 35: None, 47: None, 51:
None, 21: None, 23: None, 25: None, 27: None}, 20: {2: None, 36: None,
38: None, 40: None, 16: None, 18: None, 52: None, 28: None, 30: None},
21: {37: None, 39: None, 41: None, 17: None, 19: None, 53: None, 29:
None, 31: None}, 22: {3: None, 36: None, 38: None, 42: None, 16: None,
18: None, 54: None, 28: None, 30: None}, 23: {37: None, 39: None, 43:
None, 17: None, 19: None, 55: None, 29: None, 31: None}, 24: {4: None,
40: None, 42: None, 16: None, 18: None, 56: None, 36: None, 28: None,
30: None}, 25: {37: None, 41: None, 43: None, 17: None, 19: None, 57:
None, 29: None, 31: None}, 26: {5: None, 38: None, 40: None, 42: None,
16: None, 18: None, 58: None, 28: None, 30: None}, 27: {39: None, 41:
None, 43: None, 17: None, 19: None, 59: None, 29: None, 31: None}, 28:
{32: None, 6: None, 44: None, 46: None, 20: None, 22: None, 24: None,
26: None, 60: None}, 29: {33: None, 45: None, 47: None, 21: None, 23:
None, 25: None, 27: None, 61: None}, 30: {34: None, 7: None, 44: None,
46: None, 20: None, 22: None, 24: None, 26: None, 62: None}, 31: {35:
None, 45: None, 47: None, 21: None, 23: None, 25: None, 27: None, 63:
None}, 32: {64: None, 36: None, 38: None, 8: None, 42: None, 16: None,
40: None, 18: None, 28: None}, 33: {65: None, 37: None, 39: None, 41:
None, 43: None, 17: None, 19: None, 29: None}, 34: {66: None, 36:
None, 38: None, 40: None, 9: None, 42: None, 16: None, 18: None, 30:
None}, 35: {67: None, 37: None, 39: None, 41: None, 43: None, 17:
None, 19: None, 31: None}, 36: {32: None, 34: None, 68: None, 10:
None, 44: None, 46: None, 20: None, 22: None, 24: None}, 37: {33:
None, 35: None, 69: None, 45: None, 47: None, 21: None, 23: None, 25:
None}, 38: {32: None, 34: None, 70: None, 11: None, 44: None, 46:
None, 20: None, 22: None, 26: None}, 39: {33: None, 35: None, 71:
None, 45: None, 47: None, 21: None, 23: None, 27: None}, 40: {32:
None, 34: None, 72: None, 44: None, 12: None, 46: None, 20: None, 24:
None, 26: None}, 41: {33: None, 35: None, 73: None, 45: None, 47:
None, 21: None, 25: None, 27: None}, 42: {32: None, 34: None, 74:
None, 44: None, 13: None, 46: None, 22: None, 24: None, 26: None}, 43:
{33: None, 35: None, 75: None, 45: None, 47: None, 23: None, 25: None,
27: None}, 44: {36: None, 38: None, 40: None, 42: None, 76: None, 14:
None, 16: None, 28: None, 30: None}, 45: {37: None, 39: None, 41:
None, 43: None, 77: None, 17: None, 29: None, 31: None}, 46: {36:
None, 38: None, 40: None, 42: None, 78: None, 15: None, 18: None, 28:
None, 30: None}, 47: {37: None, 39: None, 41: None, 43: None, 79:
None, 19: None, 29: None, 31: None}, 48: {16: None, 79: None}, 49:
{17: None, 78: None}, 50: {18: None, 77: None}, 51: {19: None, 76:
None}, 52: {75: None, 20: None}, 53: {74: None, 21: None}, 54: {73:
None, 22: None}, 55: {72: None, 23: None}, 56: {24: None, 71: None},
57: {25: None, 70: None}, 58: {26: None, 69: None}, 59: {27: None, 68:
None}, 60: {67: None, 28: None}, 61: {66: None, 29: None}, 62: {65:
None, 30: None}, 63: {64: None, 31: None}, 64: {32: None, 63: None},
65: {33: None, 62: None}, 66: {34: None, 61: None}, 67: {35: None, 60:
None}, 68: {59: None, 36: None}, 69: {58: None, 37: None}, 70: {57:
None, 38: None}, 71: {56: None, 39: None}, 72: {40: None, 55: None},
73: {41: None, 54: None}, 74: {42: None, 53: None}, 75: {43: None, 52:
None}, 76: {51: None, 44: None}, 77: {50: None, 45: None}, 78: {49:
None, 46: None}, 79: {48: None, 47: None}}

Pi = [[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15], [16, 17,
18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34,
35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47], [48, 49, 50, 51,
52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68,
69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79]]

****************************

G = {0: {5: None, 6: None, 7: None, 9: None, 10: None}, 1: {3: None,
4: None, 11: None, 12: None, 13: None, 18: None}, 2: {3: None, 4:
None, 11: None, 12: None, 14: None, 20: None}, 3: {1: None, 2: None,
4: None, 13: None, 14: None, 22: None}, 4: {1: None, 2: None, 3: None,
13: None, 14: None, 24: None}, 5: {0: None, 7: None, 8: None, 9: None,
15: None, 26: None}, 6: {0: None, 7: None, 8: None, 10: None, 15:
None, 28: None}, 7: {0: None, 5: None, 6: None, 9: None, 10: None, 30:
None}, 8: {32: None, 5: None, 6: None, 9: None, 10: None, 15: None},
9: {0: None, 34: None, 5: None, 7: None, 8: None, 15: None}, 10: {0:
None, 36: None, 6: None, 7: None, 8: None, 15: None}, 11: {1: None, 2:
None, 38: None, 12: None, 13: None, 14: None}, 12: {1: None, 2: None,
40: None, 11: None, 13: None, 14: None}, 13: {1: None, 3: None, 4:
None, 42: None, 11: None, 12: None}, 14: {2: None, 3: None, 4: None,
44: None, 11: None, 12: None}, 15: {5: None, 6: None, 8: None, 9:
None, 10: None, 46: None}, 16: {39: None, 41: None, 42: None, 44:
None, 48: None, 18: None, 20: None, 22: None, 24: None}, 17: {38:
None, 40: None, 43: None, 45: None, 49: None, 19: None, 21: None, 23:
None, 25: None}, 18: {32: None, 1: None, 34: None, 37: None, 46: None,
16: None, 50: None, 26: None, 29: None, 30: None}, 19: {33: None, 35:
None, 36: None, 47: None, 17: None, 51: None, 27: None, 28: None, 31:
None}, 20: {32: None, 2: None, 35: None, 36: None, 46: None, 16: None,
52: None, 27: None, 28: None, 30: None}, 21: {33: None, 34: None, 37:
None, 47: None, 17: None, 53: None, 26: None, 29: None, 31: None}, 22:
{33: None, 34: None, 3: None, 36: None, 47: None, 16: None, 54: None,
26: None, 28: None, 30: None}, 23: {32: None, 35: None, 37: None, 46:
None, 17: None, 55: None, 27: None, 29: None, 31: None}, 24: {33:
None, 34: None, 4: None, 47: None, 16: None, 56: None, 36: None, 26:
None, 28: None, 30: None}, 25: {32: None, 35: None, 37: None, 46:
None, 17: None, 57: None, 27: None, 29: None, 31: None}, 26: {5: None,
38: None, 40: None, 42: None, 45: None, 18: None, 21: None, 22: None,
24: None, 58: None}, 27: {39: None, 41: None, 43: None, 44: None, 19:
None, 20: None, 23: None, 25: None, 59: None}, 28: {6: None, 38: None,
40: None, 43: None, 44: None, 19: None, 20: None, 22: None, 24: None,
60: None}, 29: {39: None, 41: None, 42: None, 45: None, 18: None, 21:
None, 23: None, 25: None, 61: None}, 30: {7: None, 41: None, 42: None,
39: None, 44: None, 18: None, 20: None, 22: None, 24: None, 62: None},
31: {38: None, 40: None, 43: None, 45: None, 19: None, 21: None, 23:
None, 25: None, 63: None}, 32: {64: None, 38: None, 8: None, 42: None,
44: None, 40: None, 18: None, 20: None, 23: None, 25: None}, 33: {65:
None, 39: None, 41: None, 43: None, 45: None, 19: None, 21: None, 22:
None, 24: None}, 34: {66: None, 38: None, 40: None, 9: None, 42: None,
45: None, 18: None, 21: None, 22: None, 24: None}, 35: {67: None, 39:
None, 41: None, 43: None, 44: None, 19: None, 20: None, 23: None, 25:
None}, 36: {68: None, 38: None, 40: None, 10: None, 43: None, 44:
None, 19: None, 20: None, 22: None, 24: None}, 37: {69: None, 39:
None, 41: None, 42: None, 45: None, 18: None, 21: None, 23: None, 25:
None}, 38: {32: None, 34: None, 36: None, 70: None, 11: None, 46:
None, 17: None, 26: None, 28: None, 31: None}, 39: {33: None, 35:
None, 37: None, 71: None, 47: None, 16: None, 27: None, 29: None, 30:
None}, 40: {32: None, 34: None, 36: None, 72: None, 12: None, 46:
None, 17: None, 26: None, 28: None, 31: None}, 41: {33: None, 35:
None, 37: None, 73: None, 47: None, 16: None, 27: None, 29: None, 30:
None}, 42: {32: None, 34: None, 37: None, 74: None, 13: None, 46:
None, 16: None, 26: None, 29: None, 30: None}, 43: {33: None, 35:
None, 36: None, 75: None, 47: None, 17: None, 27: None, 28: None, 31:
None}, 44: {32: None, 35: None, 36: None, 76: None, 14: None, 16:
None, 46: None, 27: None, 28: None, 30: None}, 45: {33: None, 34:
None, 37: None, 77: None, 47: None, 17: None, 26: None, 29: None, 31:
None}, 46: {38: None, 40: None, 42: None, 44: None, 78: None, 15:
None, 18: None, 20: None, 23: None, 25: None}, 47: {39: None, 41:
None, 43: None, 45: None, 79: None, 19: None, 21: None, 22: None, 24:
None}, 48: {64: None, 16: None, 79: None}, 49: {65: None, 78: None,
17: None}, 50: {18: None, 52: None, 77: None}, 51: {19: None, 76:
None, 53: None}, 52: {50: None, 75: None, 20: None}, 53: {74: None,
51: None, 21: None}, 54: {73: None, 22: None, 70: None}, 55: {72:
None, 71: None, 23: None}, 56: {24: None, 72: None, 71: None}, 57:
{25: None, 70: None, 73: None}, 58: {26: None, 60: None, 69: None},
59: {27: None, 68: None, 61: None}, 60: {58: None, 67: None, 28:
None}, 61: {66: None, 59: None, 29: None}, 62: {65: None, 78: None,
30: None}, 63: {64: None, 79: None, 31: None}, 64: {48: None, 32:
None, 63: None}, 65: {49: None, 62: None, 33: None}, 66: {34: None,
68: None, 61: None}, 67: {35: None, 60: None, 69: None}, 68: {66:
None, 59: None, 36: None}, 69: {58: None, 67: None, 37: None}, 70:
{57: None, 38: None, 54: None}, 71: {56: None, 55: None, 39: None},
72: {40: None, 56: None, 55: None}, 73: {41: None, 54: None, 57:
None}, 74: {42: None, 76: None, 53: None}, 75: {43: None, 52: None,
77: None}, 76: {74: None, 51: None, 44: None}, 77: {50: None, 75:
None, 45: None}, 78: {49: None, 62: None, 46: None}, 79: {48: None,
63: None, 47: None}}

Pi = [[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15], [16, 17,
18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34,
35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47], [48, 49, 50, 51,
52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68,
69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79]]
--~--~---------~--~----~------------~-------~--~----~
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