Using Emacs and Proof General, Unicode symbols can be conveniently entered using the TeX input method.
Just do M-x set-input-method and choose TeX. Unicode symbols can then be entered using TeX macros, e.g. "\beta" for "β", "_1" for "₁", "\circ" for "∘", etc.
To make this happen automatically, add the following line to your .emacs file:
(add-hook 'proof-mode-hook (lambda () (set-input-method "TeX") ))
In CoqIDE (using UIM on POSIX systems)
On CoqIDE, under Unix systems (Linux, BSD, MacOS X), the TeX input method is also available thanks to the UIM input method library.
You need uim 1.5.x or 1.6.x installed.
With uim 1.6.x, the TeX input method works out of the box
To configure uim, execute the command uim-pref-gtk as a regular user. In the Global Settings group set the default Input Method to ELatin (don’t forget to tick the checkbox Specify default IM). In the ELatin group set the layout to TeX, and remember the content of the [ELatin] on field (by default <Control>). You can now execute CoqIDE with the following command (assuming you use a Bourne-style shell):
# the next line tells to use uim as default input method framework (otherwise, you'll have to choose manually the input method from CoqIDE by using the button-right menu)
$ export GTK_IM_MODULE=uim
# Start coqide
If not already activated, activate the ELatin Input Method with "Ctrl-\", then type the sequence "\beta". You will see the sequence being replaced by β as soon as you type the "a".
With uim 1.5.x, the TeX input method is not included and you need first to install it. Take the attached files coqide-custom.scm, coqide-rules.scm and coqide.scm and install them in the repository of input methods for uim (typically /usr/share/uim if uim was installed using a standard Linux distribution). Call first the command uim-register --register coqide to register the new files, then, proceed as above, except that you have to select CoqIDE instead of ELatin in the Global Settings of uim-pref-gtk. If not already done automatically, you might have first to edit the set of Enabled input methods to add CoqIDE to this set.
Many thanks to Vincent Gross for making this input method available.
Alternative input methods
See XCompose and notations for using the XCompose method (XIM) under X-windows.