From 46f34181e3dbbb691d3c9a7239b08e8665a994a4 Mon Sep 17 00:00:00 2001
From: Erik Demaine <edemaine@mit.edu>
Date: Thu, 11 May 2017 16:03:37 -0400
Subject: [PATCH] Add \iff, \implies, \impliedby support. Fix #190.

* Based on @ronkok's code, but without \mathrel as it's absent
  from amstex.sty.
* Add toBuild tests to ensure these operators expand.
---
 src/macros.js      | 9 +++++++++
 test/katex-spec.js | 8 +++++++-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/src/macros.js b/src/macros.js
index fb1054bf..ec7b90ce 100644
--- a/src/macros.js
+++ b/src/macros.js
@@ -21,3 +21,12 @@ defineMacro("\\endgroup", "}");
 // \def\overset#1#2{\binrel@{#2}\binrel@@{\mathop{\kern\z@#2}\limits^{#1}}}
 defineMacro("\\overset", "\\mathop{#2}\\limits^{#1}");
 defineMacro("\\underset", "\\mathop{#2}\\limits_{#1}");
+
+//TODO: When implementing \dots, should ideally add the \DOTSB indicator
+//      into the macro, to indicate these are binary operators.
+// \def\iff{\DOTSB\;\Longleftrightarrow\;}
+// \def\implies{\DOTSB\;\Longrightarrow\;}
+// \def\impliedby{\DOTSB\;\Longleftarrow\;}
+defineMacro("\\iff", "\\;\\Longleftrightarrow\\;");
+defineMacro("\\implies", "\\;\\Longrightarrow\\;");
+defineMacro("\\impliedby", "\\;\\Longleftarrow\\;");
diff --git a/test/katex-spec.js b/test/katex-spec.js
index 651df70e..caefcc0a 100644
--- a/test/katex-spec.js
+++ b/test/katex-spec.js
@@ -2012,12 +2012,18 @@ describe("A macro expander", function() {
         });
     });
 
-    it("should expand the \overset macro as expected", function() {
+    it("should expand the \\overset macro as expected", function() {
         expect("\\overset?=").toParseLike("\\mathop{=}\\limits^{?}");
         expect("\\overset{x=y}{\sqrt{ab}}")
             .toParseLike("\\mathop{\sqrt{ab}}\\limits^{x=y}");
         expect("\\overset {?} =").toParseLike("\\mathop{=}\\limits^{?}");
     });
+
+    it("should build \\iff, \\implies, \\impliedby", function() {
+        expect("X \\iff Y").toBuild();
+        expect("X \\implies Y").toBuild();
+        expect("X \\impliedby Y").toBuild();
+    });
 });
 
 describe("A parser taking String objects", function() {