disallow '-' and '$' in variable names
diff --git a/asterix-app/src/test/resources/AQLTS/queries/variables.aql b/asterix-app/src/test/resources/AQLTS/queries/variables.aql
new file mode 100644
index 0000000..9e9a82d
--- /dev/null
+++ b/asterix-app/src/test/resources/AQLTS/queries/variables.aql
@@ -0,0 +1,4 @@
+let $a:=1
+let $b:=1
+return
+  $b-$a
\ No newline at end of file
diff --git a/asterix-aql/src/main/javacc/AQL.jj b/asterix-aql/src/main/javacc/AQL.jj
index 250a07e..f2fa66c 100644
--- a/asterix-aql/src/main/javacc/AQL.jj
+++ b/asterix-aql/src/main/javacc/AQL.jj
@@ -1540,7 +1540,7 @@
 	VarIdentifier var = new VarIdentifier();
 }
 {
-      <VARIABLE>
+  <VARIABLE>
     {
      String varName = token.image; 
      Identifier ident = lookupSymbol(varName);
@@ -1565,7 +1565,7 @@
 	VarIdentifier var = new VarIdentifier();
 }
 {
-      <VARIABLE>
+  <VARIABLE>
     {
      Identifier ident = lookupSymbol(token.image);
      if(ident != null) { // exist such ident
@@ -2205,7 +2205,7 @@
 <DEFAULT>
 TOKEN :
 {
-	<VARIABLE : "$" <IDENTIFIER> >
+	<VARIABLE : "$" (<LETTER>)+ (<LETTER> | <DIGIT> | "_")* >
 }
 
 SKIP: