Retracted: Use the path github.com/open-policy-agent/opa (lower-case), not github.com/open-policy-agent/OPA.
Before 0.15.0 OPA was not using go modules and the correct import path was not enforced.
Truth implements post-processing on raw traces. The goal of the
post-processing is to produce a filtered version of the trace that shows why
the top-level query was true.