Fix typo

doc/RTD/source/Task/locks.rst

@@ -14,11 +14,11 @@ concurrently, even if the tasks have no dependencies between them.
 For this reason, each task locks the data it works on when it begins,
 and unlocks the data again once it's finished. Data here refers to the
 particle (gas, gravity, stars,...) content of a cell as well as of the
-hierarchy of cells in the tree at levels closer to the root that.  By
-default, it is assumed that the task is doing work on hydro
-particles. If your task requires other particle types, you will need
-to specify that in ``src/task.c``. Suppose you have implemented a task
-with type ``task_type_new`` that requires both stars and hydro
+hierarchy of cells in the tree at levels closer to the root than the
+cell itself.  By default, it is assumed that the task is doing work on
+hydro particles. If your task requires other particle types, you will
+need to specify that in ``src/task.c``. Suppose you have implemented a
+task with type ``task_type_new`` that requires both stars and hydro
 particles: ::