aloiscochard/shapeless — comment on commit d0bb2df0efda008f4af87735fbf399486783f1de
File: src/main/scala/shapeless/hlist.scala line 667
By milessabin:

Why `H <: U`? Why not have,
```implicit def hlistFilter[H, L <: HList, H, Out <: HList]
(implicit aux : FilterAux[L, H, Out]) = new FilterAux[H :: L, H, H :: Out]
```
It's marginally simpler, passes the tests and is more consistent with eg. `select[U]`.