code: public ClassInfoList exclude(final ClassInfoList other) {
          final Set<ClassInfo> reachableClassesDifference = new LinkedHashSet<>(this);
          final Set<ClassInfo> directlyRelatedClassesDifference = new LinkedHashSet<>(directlyRelatedClasses);
          reachableClassesDifference.removeAll(other);
          directlyRelatedClassesDifference.removeAll(other.directlyRelatedClasses);
          return new ClassInfoList(reachableClassesDifference, directlyRelatedClassesDifference, sortByName);
      }
docs: Find the set difference between this {@link ClassInfoList} and another {@link ClassInfoList}, i.e. (this \
  other).
  
  @param other
  The other {@link ClassInfoList} to subtract from this one.
  @return The set difference of this {@link ClassInfoList} and other, i.e. (this \ other).