+/**
+ * Mark elements as "seen" using a hash of the element. Not supported
+ * by all block plugins.
+ *
+ * @param bg group to update
+ * @param seen_results results already seen
+ * @param seen_results_count number of entries in @a seen_results
+ */
+typedef void
+(*GNUNET_BLOCK_GroupMarkSeenFunction)(struct GNUNET_BLOCK_Group *bg,
+ const struct GNUNET_HashCode *seen_results,
+ unsigned int seen_results_count);
+
+
+/**
+ * Merge two groups, if possible. Not supported by all block plugins,
+ * can also fail if the nonces were different.
+ *
+ * @param bg1 group to update
+ * @param bg2 group to merge into @a bg1
+ * @return #GNUNET_OK on success, #GNUNET_NO if the nonces were different and thus
+ * we failed.
+ */
+typedef int
+(*GNUNET_BLOCK_GroupMergeFunction)(struct GNUNET_BLOCK_Group *bg1,
+ const struct GNUNET_BLOCK_Group *bg2);
+
+