`config.json` should specify six of Lean's [key features](https://exercism.org/docs/building/tracks/config-json#h-key-features). For comparison: - [Haskell](https://github.com/exercism/haskell/blob/6d8a6cbe9964859f0b32cd7ae75b110f6c8b723a/config.json#L1413) - [Idris](https://github.com/exercism/idris/blob/5926a1a2545440659acf27da5da4ce9858fd6bd7/config.json#L517) - [Julia](https://github.com/exercism/julia/blob/cec0dd57ac47d48ecc4d2e01b9b258be08b346ce/config.json#L1894)
