Goal 0.3 -- check off the DPJ commutative keyword uses

[rrnewton]

Here are the DPJ benchmarks:

https://github.com/dpj/DPJ/tree/master/Benchmarks

When they do reductions they use a "commutaitve" keyword as a programmer assertion. For instance here and here.

We can use this in an evaluation section -- "what would it take to make all the DPJ examples fully safe, rather than trusting the programmer?".