feat(emacs/lean-input): add not(¬) and iff(↔)

close leanprover/tutorial#81

src/emacs/lean-input.el

@@ -194,6 +194,10 @@ order for the change to take effect."
 (defcustom lean-input-translations
   (let ((max-lisp-eval-depth 2800)) `(
 
+  ;; Negation
+
+  ("not" . ("¬"))
+
   ;; Equality and similar symbols.
 
   ("eq"  . ,(lean-input-to-string-list "=∼∽≈≋∻∾∿≀≃⋍≂≅ ≌≊≡≣≐≑≒≓≔≕≖≗≘≙≚≛≜≝≞≟≍≎≏≬⋕"))
@@ -378,7 +382,7 @@ order for the change to take effect."
   ("join"     . ,(lean-input-to-string-list "⋈⋉⋊⋋⋌⨝⟕⟖⟗"))
 
   ;; Arrows.
-
+  ("iff" . ("↔"))
   ("l"  . ,(lean-input-to-string-list "λ←⇐⇚⇇⇆↤⇦↞↼↽⇠⇺↜⇽⟵⟸↚⇍⇷ ↹     ↢↩↫⇋⇜⇤⟻⟽⤆↶↺⟲                                     "))
   ("r"  . ,(lean-input-to-string-list "→⇒⇛⇉⇄↦⇨↠⇀⇁⇢⇻↝⇾⟶⟹↛⇏⇸⇶ ↴    ↣↪↬⇌⇝⇥⟼⟾⤇↷↻⟳⇰⇴⟴⟿ ➵➸➙➔➛➜➝➞➟➠➡➢➣➤➧➨➩➪➫➬➭➮➯➱➲➳➺➻➼➽➾⊸"))
   ("u"  . ,(lean-input-to-string-list "↑⇑⟰⇈⇅↥⇧↟↿↾⇡⇞          ↰↱➦ ⇪⇫⇬⇭⇮⇯                                           "))