rulebook-core/src/main/java/com/deliveredtechnologies/rulebook/StandardDecision.java
@Override
  @SuppressWarnings("unchecked")
  public Decision<T, U> using(String... factNames) {
    _rule.using(factNames);
    return this;
  }
@Override
  @SuppressWarnings("unchecked")
  public Decision<T, U> using(String... factNames) {
    _rule.using(factNames);
    return this;
  }
The using() method reduces the facts to those specifically named here.
The using() method only applies to the then() method immediately following it.
@param factNames the names of the facts to be used
@return          the current object