Dear Stefan,
Thanks for your help!
I tried as you say, and the result was that I got the message
D-Bus error: "Emacs not compiled with dbus support"
in the minibuffer.
Actually, the freeze did not happen.
I mean, the situation seemed to be the same as before entering `M-x eval-buffer RET`.
Maybe the word "freeze" was inappropriate.
What I wanted to convey is as follows.
I did "I-search" (C-s) then "proof-assert-next-command-interactive" (C-c C-n),
but the proof process got stuck.
Here, "got stuck" means that Emacs did not go out of the proof process for several minutes.
During that situation, I could move the cursor but I could not interrupt the proof process by Quit/C-g or tool-bar interrupt.
The backtrace that I sent earlier was shown immediately after the proof process was over,
say, several minutes after Emacs got stuck.
I apologize if my explanation is confusing, since I am not so fluent in English.