Failure for very simple cases

[zyong812]

sng_parser.tprint(sng_parser.parse('the chair is in front of the desk'))
Entities:
+--------+-----------+-------------+
| Head   | Span      | Modifiers   |
|--------+-----------+-------------|
| chair  | the chair | the         |
| desk   | the desk  | the         |
+--------+-----------+-------------+
Relations:
+-----------+------------+----------+
| Subject   | Relation   | Object   |
|-----------+------------+----------|
+-----------+------------+----------+