One of many available InputMethods for entering Unicode text, the TeX input method allows you to enter Unicode characters by typing in sequences reminiscent of those used for input by the typesetting language TeX. For example, typing \lambda inserts a λ.

As would be expected, this input method may be invoked with ‘M-x set-input-method’ and entering ‘TeX’.

A list of available sequences may be viewed with ‘M-x describe-input-method’

Customizing the TeX Input Method

Here is an example. You need to bind the “current” package before calling ‘quail-define-rules’ and you need to use the ‘append’ annotation. You can add more rules to this function call.

  (activate-input-method "TeX") ;; the input method has to be triggered for `quail-package-alist' to be non-nil
  (let ((quail-current-package (assoc "TeX" quail-package-alist)))
   (quail-define-rules ((append . t))
                       ("^\\alpha" ?ᵅ))))

An alternative to the TeX input method

Using the package ‘math-symbol-lists’ (available on MELPA), one can define a more comprehensive mathematical input method, containing all symbols and characters defined in the ‘unicode-math’ LaTeX package. This includes a myriad of symbols, alternative alphabets, and accents. Install the ‘math-symbol-lists’ package and add the following to your init file

(require 'math-symbol-lists)
(quail-define-package "math" "UTF-8" "Ω" t)
(quail-define-rules ; add whatever extra rules you want to define here...
 ("\\from"    #X2190)
 ("\\to"      #X2192)
 ("\\lhd"     #X22B2)
 ("\\rhd"     #X22B3)
 ("\\unlhd"   #X22B4)
 ("\\unrhd"   #X22B5))
(mapc (lambda (x)
        (if (cddr x)
            (quail-defrule (cadr x) (car (cddr x)))))
      (append math-symbol-list-basic math-symbol-list-extended))

To activate the input method, type `C-u C-\ math RET’. Then, typing \mscrC yields 𝒞, \lParen yields ⦅, \gamma\dot yields γ̇, etc