Update README.md

Author: ws-garcia

README.md

@@ -35,7 +35,7 @@ Expression    =     ([{"("}]  SubExpr [{Operator [{"("}] SubExpr [{")"}]}] [{")"
 SubExpr       =     Token [{Operator Token}]
 Token         =     [{Unary}] Argument [(Operator | Function) ["("] [{Unary}] [Argument] [")"]]
 Argument      =     (List | Variable | Operand)
-List          =     {["{"] SubExpr [{";" SubExpr}] ["}"]} 
+List          =     "{" ["{"] SubExpr [{";" SubExpr}] ["}"] "}"
 Unary         =     "-" | "+" | ~
 Operand       =     ({Digit} ["."] [{Digit}] ["E"("-" | "+"){Digit}] | (True | False))
 Variable      =     Alphabet [{Decimal}] [{(Digit | Alphabet)}]