Update README.md

Author: ws-garcia

README.md

@@ -38,7 +38,7 @@ Expression    =     ([{"("}]  SubExpr [{Operator [{"("}] SubExpr [{")"}]}] [{")"
 SubExpr       =     Token [{Operator Token}]
 Token         =     [{Unary}] Argument [(Operator | Function) ["("] [{Unary}] [Argument] [")"]]
 Argument      =     (List | Variable | Operand | Literal)
-List          =     "{" ["{"] SubExpr [{";" SubExpr}] ["}"] "}"
+List          =     ["{"] ["{"] SubExpr [{";" SubExpr}] ["}"] ["}"]
 Unary         =     "-" | "+" | ~
 Literal       =     (Operand | "'"Alphabet"'")
 Operand       =     ({Digit} ["."] [{Digit}] ["E"("-" | "+"){Digit}] | (True | False))