emacs-gtk, emacs-lucid and emacs-nox have "emacs" in "Provides:".
It should be versioned, so that they match a versioned dependency.

The issue is the following. I have the emacs-gtk package installed,
but not the "emacs" metapackage (it is useless). The elpa-transient
package, which is not installed, recommends "emacs (>= 1:25.1)". If
I want to install it, apt wants to install "emacs" too[*] because it
assumes that the "emacs" version provided by emacs-gtk may be too
low. To avoid the useless "emacs" installation, the provided "emacs"
needs to be versioned, normally with the same version as emacs-gtk,
emacs-lucid and emacs-nox; thus it will match the ">= 1:25.1"
condition.

[*] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1007122