Update advancedSymbols.js

add nexist symbol
diff --git a/src/commands/math/advancedSymbols.js b/src/commands/math/advancedSymbols.js
index 776b9a7..be115ad 100644
--- a/src/commands/math/advancedSymbols.js
+++ b/src/commands/math/advancedSymbols.js
@@ -303,6 +303,9 @@
 LatexCmds.xist = //LOL
 LatexCmds.xists = LatexCmds.exist = LatexCmds.exists =
   bind(VanillaSymbol,'\\exists ','∃');
+  
+LatexCmds.nexists = LatexCmds.nexist =
+      bind(VanillaSymbol, '\\nexist ', '∄');
 
 LatexCmds.and = LatexCmds.land = LatexCmds.wedge =
   bind(VanillaSymbol,'\\wedge ','∧');