1 | initial version |

The program doesn't use any sage-specific functionality, and it doesn't have to. You can just use any correct python implementation. For instance, the algorithm on the wikipedia page https://en.wikipedia.org/wiki/De_Bruijn_sequence has probably been looked at quite a bit, so may well be correct (I didn't check completely, but its output does contain the string "hccc")

2 | No.2 Revision |

The program doesn't use any sage-specific functionality, and it doesn't have to. You can just use any correct python implementation. ~~For instance, ~~The routine presented seems like a verbatim copy of the ~~algorithm ~~one on https://en.wikipedia.org/wiki/De_Bruijn_sequence . Note that the ~~wikipedia page https://en.wikipedia.org/wiki/De_Bruijn_sequence has probably been looked at quite ~~definition of a ~~bit, so may well ~~"de bruijn sequence" includes it's a *cyclic* sequence. So you should be ~~correct (I didn't check completely, but its output does contain ~~appending the ~~string "hccc")~~head of the sequence to the tail:

```
"hccc" in seq+seq[:3]
```

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