There's a passage in the "MPI Scatter, Gather, and Allgather" tutorial that says the following in regards to the MPI_Scatter(() function:

In practice, send_count is often equal to the number of elements in the array divided by the number of processes. What’s that you say? The number of elements isn’t divisible by the number of processes? Don’t worry, we will cover that in a later lesson :-)

Which lesson is this referring to? I wasn't able to find this topic in any of the subsequent lessons.