I tried to install drom via opam and got told that it conflicted with core_kernel:

  ⊘ remove  core_kernel      v0.14.1        [conflicts with opam-file-format]
  ↗ upgrade opam-file-format 2.1.0 to 2.1.1 [required by drom_lib]

but `opam show core_kernel` lists no dependency on opam-file-format`, and `opam show opam-file-format.2.1.1` just says

  depends:      "ocaml" "dune" {>= "2.0"} "alcotest" {with-test}
  conflicts:    "core_kernel"

with no indication as to why the conflict.

martin