  In some other papers, the Lagrangians in the causal sets included
coefficients that were to be computed by integrating over Alexandrov set. In
those other papers, this integral was explicitly evaluated, which resulted in
rather sophisticated expressions. On the other hand, in this paper, instead of
evaluating this integral, it was left in an integral form where the actual
fields were replaced with test functions (thus avoiding nonlinearities). The
test functions get absorbed into equations in a very natural way, so the
resulting formulas look elegant.
