A while ago I’ve blogged about that very same question here:
- Who discovered the Leech lattice?
- So, who discovered the Leech lattice?
- Erna Bannow, octonions and the Leech
The summary of these posts being that I thought it was rather unlikely for Witt to have discovered the Leech lattice.
However, using the same sources, Borcherds rates a more than 90% probability for Witt to have indeed discovered the Leech lattice in 1940.
His evidence for this is:
- Witt said he discovered it.
- His construction (in his 1972 colloquium talk) is unlike any other construction of the Leech lattice.
- Witt was the expert on Steiner systems, and the system S(5,8,24) is crucial in Leech’s construction of his lattice.