gistfile1.txt

sudo nix-channel --list
nixos https://nixos.org/channels/nixos-unstable
nixos-1803 https://nixos.org/channels/nixos-18.03
nixos-1809 https://nixos.org/channels/nixos-18.09
nixos-1903 https://nixos.org/channels/nixos-19.03
nixos-stable https://nixos.org/channels/nixos-18.09
nixos-unstable https://nixos.org/channels/nixos-unstable

tricky-channels.nix

with import <nixpkgs> { };
{
  unstable = import <nixos-unstable> { config = { allowUnfree = true; }; };

  stable = import <nixos-stable> { config = { allowUnfree = true; }; };

  nixos-1803 = import <nixos-1803> { config = { allowUnfree = true; }; };

  nixos-1809 = import <nixos-1809> { config = { allowUnfree = true; }; };

  nixos-1903 = import <nixos-1903> { config = { allowUnfree = true; }; };
}