diff --git a/doc/environments/groupthm/groupthm.dtx b/doc/environments/groupthm/groupthm.dtx
index 0002ac8..6cbcf0d 100644
--- a/doc/environments/groupthm/groupthm.dtx
+++ b/doc/environments/groupthm/groupthm.dtx
@@ -1878,8 +1878,42 @@
 % \end{macro}
 % 
 % 
-% 
-% 
+%
+% \begin{macro}{\@@_flatten_groups_hierarchy:nN}
+%    \begin{syntax}
+%       \cs{@@_flatten_groups_hierarchy:n}\marg{theorem groups}\marg{clist}
+%    \end{syntax}
+%		 
+%     Expects a comma separated list of \meta{theorem group}s.
+%     The inheritance relation is flattened, and the set of 
+%     obtained theorem groups is stored in \meta{clist}
+%
+%    \begin{macrocode}
+\cs_new:Npn \@@_push_tmpa_seq:n #1
+  {
+    \seq_push:Nn \l_tmpa_seq { #1 }
+  }
+\cs_new:Npn \@@_flatten_groups_hierarchy:nN #1 #2
+  {
+    \clist_clear:N #2
+    \seq_set_from_clist:Nn \l_tmpa_seq { #1 }
+    \bool_until_do:nn
+      {
+        \seq_if_empty_p:N \l_tmpa_seq
+      }
+      {
+        \seq_pop:NN \l_tmpa_seq \l_tmpa_tl
+        \clist_if_in:NVF #2 \l_tmpa_tl
+          {
+            \clist_put_left:NV #2 \l_tmpa_tl
+            \clist_map_function:cN
+              { g_@@_parents_group__ \l_tmpa_tl __clist }
+              \@@_push_tmpa_seq:n
+          }
+      }
+  }
+%    \end{macrocode}
+% \end{macro}
 % 
 % 
 % \subsection{Iterating over powersets}
diff --git a/doc/environments/groupthm/groupthm.sty b/doc/environments/groupthm/groupthm.sty
index cd68056..b6cddf7 100644
--- a/doc/environments/groupthm/groupthm.sty
+++ b/doc/environments/groupthm/groupthm.sty
@@ -379,6 +379,29 @@
   {
     \groupthm_add_parent:nn { #1 } { #2 }
   }
+\cs_new:Npn \__groupthm_push_tmpa_seq:n #1
+  {
+    \seq_push:Nn \l_tmpa_seq { #1 }
+  }
+\cs_new:Npn \__groupthm_flatten_groups_hierarchy:nN #1 #2
+  {
+    \clist_clear:N #2
+    \seq_set_from_clist:Nn \l_tmpa_seq { #1 }
+    \bool_until_do:nn
+      {
+        \seq_if_empty_p:N \l_tmpa_seq
+      }
+      {
+        \seq_pop:NN \l_tmpa_seq \l_tmpa_tl
+        \clist_if_in:NVF #2 \l_tmpa_tl
+          {
+            \clist_put_left:NV #2 \l_tmpa_tl
+            \clist_map_function:cN
+              { g__groupthm_parents_group__ \l_tmpa_tl __clist }
+              \__groupthm_push_tmpa_seq:n
+          }
+      }
+  }
 \clist_new:N  \l__powerset_copied_clist
 \seq_new:N    \l__powerset_saved_seq
 \cs_generate_variant:Nn \clist_remove_all:Nn { N V }