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| 1 | +# $S_6$ as a subgroup of the McLaughlin group McL |
| 2 | + |
| 3 | +The presentation and subgroup generators on this page come from presentation |
| 4 | +(11.1) in [Đoković's paper](https://doi.org/10.1017/S1446788700030068). |
| 5 | + |
| 6 | +## Claim |
| 7 | + |
| 8 | +If |
| 9 | + |
| 10 | +$$ |
| 11 | + H=\langle a,b,c,e,f\rangle \cong S_6, |
| 12 | +$$ |
| 13 | + |
| 14 | +then |
| 15 | + |
| 16 | +$$ |
| 17 | + [\mathrm{McL}:H]=1,247,400. |
| 18 | +$$ |
| 19 | + |
| 20 | +We verify the claimed index, but not the claimed isomorphism type. The shared |
| 21 | +presentation adds ten relations listed as consequences in the source. We do not |
| 22 | +verify that these relations are redundant here. |
| 23 | + |
| 24 | +## The code |
| 25 | + |
| 26 | +The presentation helper is shown on the [entire enumeration page](898128000.md). |
| 27 | +The recorded run took about 8.5 seconds. |
| 28 | + |
| 29 | +```python |
| 30 | +from McL_dokovic_i import mcl_dokovic_i |
| 31 | +from libsemigroups_pybind11 import ToddCoxeter, congruence_kind |
| 32 | + |
| 33 | +p = mcl_dokovic_i() |
| 34 | + |
| 35 | +tc = ToddCoxeter(congruence_kind.onesided, p) |
| 36 | +tc.strategy(ToddCoxeter.options.strategy.felsch).use_relations_in_extra(True) |
| 37 | + |
| 38 | +tc.add_generating_pair("a", "") |
| 39 | +tc.add_generating_pair("b", "") |
| 40 | +tc.add_generating_pair("c", "") |
| 41 | +tc.add_generating_pair("e", "") |
| 42 | +tc.add_generating_pair("f", "") |
| 43 | + |
| 44 | +tc.run() |
| 45 | + |
| 46 | +print(f"The index of the subgroup is {tc.number_of_classes()}") |
| 47 | +``` |
| 48 | + |
| 49 | +## The output |
| 50 | + |
| 51 | +??? info "Truncated output from the Python script" |
| 52 | + |
| 53 | + ``` |
| 54 | + ++++++++++++++++++++++++++++++++ |
| 55 | + #0: ToddCoxeter: RUN 0 START (strategy() = felsch) |
| 56 | + #0: ToddCoxeter: |A| = 6, |R| = 28, |u| + |v| ∈ [2, 21], ∑(|u| + |v|) = 191 |
| 57 | + [... lines omitted ...] |
| 58 | + #0: ToddCoxeter: RUN 0 STOP (finished) |
| 59 | + #0: ToddCoxeter: run 0 | lookahead | lookbehind | hlt | felsch |
| 60 | + #0: ToddCoxeter: num. phases | 0 | 0 | 0 | 1 |
| 61 | + #0: ToddCoxeter: time spent in phases | - (0%) | - (0%) | - (0%) | 8.467s (100%) |
| 62 | + #0: ToddCoxeter: phase 0.1 = 8.472s | run 0 = 8.472s | all runs = 8.472s | elapsed = 8.472s |
| 63 | + The index of the subgroup is 1247400 |
| 64 | + ``` |
| 65 | + |
| 66 | +:material-checkbox-marked-circle-outline: The computed index is the claimed |
| 67 | +index: $1,247,400$. |
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