second review from Ralph

Author: JanStaschulat

_docs/concepts/client_library/execution_management/index.md

@@ -238,7 +238,8 @@ An Example of the LET concept is shown in Figure 3. Assume that two processes ar
 - co-operative scheduling of tasks within a process (sequential execution)
 - data synchronization with LET-semantics
 
-While periodic activation is possible in ROS2 by using timers, preemptive scheduling is supported by the operating system and assigning priorities on the granularity of threads/processes that correspond to the ROS nodes; it is not possible to sequentially execute callbacks, which have no data-dependency. Furthermore data is read from the DDS queue just before the callback is executed and data is written sometime during the time the application is executed. While the `spin_period` function of the rclcpp Executor allows to check for data at a fixed period and executing those callbacks for which data is available, however, with this spin-function does not execute all callbacks irrespective wheter data is available or not. So `spin_period` is not helpful to periodically execute a number of callbacks (aka tasks within a process). So we need a mechanism that triggers the execution of multiple callbacks (aka tasks) based on a timer. Data transmission is achieved via DDS which does not allow to implement a LET-semantics. To summarize, we derive the following requirements:
+
+While periodic activation is possible in ROS 2 by using timers, preemptive scheduling is supported by the operating system and assigning priorities on the granularity of threads/processes that correspond to the ROS nodes; it is not possible to sequentially execute callbacks, which have no data-dependency. Furthermore data is read from the DDS queue just before the callback is executed and data is written sometime during the time the application is executed. While the `spin_period` function of the rclcpp Executor allows to check for data at a fixed period and executing those callbacks for which data is available, however, with this spin-function does not execute all callbacks irrespective wheter data is available or not. So `spin_period` is not helpful to periodically execute a number of callbacks (aka tasks within a process). So we need a mechanism that triggers the execution of multiple callbacks (aka tasks) based on a timer. Data transmission is achieved via DDS which does not allow to implement a LET-semantics. To summarize, we derive the following requirements.
 
 **Derived requirements:**
 - trigger the execution
@@ -723,7 +724,7 @@ URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8376277&isnumber=83
 
 
 ## References
-* [S2021]<a name="S2021"></a> J. Staschulat, "Micro-ROS: The rclc Executor", ROS 2 Executor: How to make it efficient, real-time and deterministic?, ROS World, Oct. 2021, [[slides](https://ec2a4d36-bac8-4759-b25e-bb1f794177f4.filesusr.com/ugd/984e93_749e27b917a54b45b9ccb5be930841b8.pdf)] [[Video](https://www.youtube.com/embed/IazrPF3RN1U)]
+* [S2021]<a name="S2021"></a> J. Staschulat, "Micro-ROS: The rclc Executor", in Workshop ROS 2 Executor: How to make it efficient, real-time and deterministic? at ROS World, Oct. 2021, [[slides](https://ec2a4d36-bac8-4759-b25e-bb1f794177f4.filesusr.com/ugd/984e93_749e27b917a54b45b9ccb5be930841b8.pdf)] [[Video](https://www.youtube.com/embed/IazrPF3RN1U)]
 
 * [SLD2021]<a name="SLD2021"></a> J. Staschulat, R. Lange and D. N. Dasari, "Budget-based real-time Executor for Micro-ROS", arXiv Pre-Print, May 2021. [[paper](https://arxiv.org/abs/2105.05590)]