我正在尝试安装 MonoDevelop 版本 5.4.1.7，以便可以将其与 Mono 5.4.1.7 一起使用。
首先，我尝试按照此处的说明安装 Mono 5.4.1.7http://www.mono-project.com/download/stable/除了替换stable-bionic为stable-xenial/snapshots/5.4.1.7（Bionic 没有 5.4 快照）。这有效：
$ sudo apt install mono-complete
[...]
mono-complete is already the newest version (5.4.1.7-0xamarin5+ubuntu1604b1).
然后我尝试使用 MonoDevelop 做同样的事情。我按照这里的说明进行操作http://www.monodevelop.com/download/但我将其替换vs-bionic为vs-xenial/snapshots/5.4.1.7。这不起作用：
$ sudo apt update
[...]
All packages are up to date.
W: Conflicting distribution: https://download.mono-project.com/repo/ubuntu stable-xenial/snapshots/5.4.1.7 InRelease (expected stable-xenial/snapshots/5.4.1.7 but got xenial)
$ sudo apt install monodevelop
[...]
Package monodevelop is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'monodevelop' has no installation candidate
我也尝试过改为stable-xenial，xenial并且sudo apt update不再抛出错误，但仍然无法安装 MonoDevelop。
为什么这不起作用？如何在我的系统上安装 MonoDevelop 版本 5.4.1.7？