diff --git a/nfvsmotifs/_sd_algorithms/expand_source_SCCs.py b/nfvsmotifs/_sd_algorithms/expand_source_SCCs.py
new file mode 100644
index 00000000..1db35824
--- /dev/null
+++ b/nfvsmotifs/_sd_algorithms/expand_source_SCCs.py
@@ -0,0 +1,177 @@
+import sys
+
+sys.path.append(".")
+
+from biodivine_aeon import BooleanNetwork
+
+import nfvsmotifs
+import networkx as nx
+import itertools as it
+from nfvsmotifs.interaction_graph_utils import infer_signed_interaction_graph, _digraph_to_regulatory_graph
+from nfvsmotifs.space_utils import percolate_space, percolate_network
+from nfvsmotifs.SuccessionDiagram import SuccessionDiagram
+from networkx import DiGraph
+from nfvsmotifs.petri_net_translation import extract_variable_names, network_to_petrinet
+
+def expand_source_SCCs(sd: SuccessionDiagram, size_limit: int | None = None) -> bool:
+    """
+    See `SuccessionDiagram.expand_minimal_spaces` for documentation.
+    """
+
+    root = sd.root()
+
+    seen = set([root])
+
+    # percolate constant nodes
+    perc_space, _ = percolate_space(sd.network, {}, strict_percolation=False)
+    perc_bn = percolate_network(sd.network, perc_space)
+
+    # find source nodes
+    source_nodes = find_source_nodes(perc_bn)
+
+    # get the initial subspaces that constitute the first depth
+    initial_sub_spaces:list[dict[str,int]] = []
+    if len(source_nodes) == 0:
+        initial_sub_spaces.append(perc_space)
+    else:
+        # get source nodes combinations
+        bin_values_list = it.product(range(2), repeat=len(source_nodes)) 
+        for bin_values in bin_values_list:
+            source_comb = dict(zip(source_nodes, bin_values))
+
+            sub_space = source_comb
+            sub_space.update(perc_space)
+            initial_sub_spaces.append(sub_space)
+
+
+def perc_and_remove_constants_from_bn(bn:BooleanNetwork, space: dict[str, int]) -> BooleanNetwork:
+    """
+    Take a BooleanNetwork and percolate given space.
+    Then remove constant nodes with rules
+    A* = (A | !A)
+    B* = (B & !B)
+    and return a clean BooleanNetwork with no constant nodes.
+
+    TODO: if possible, delete constant nodes from the BooleanNetwork directly,
+    without converting into bnet and back.
+    """
+
+    perc_space, _ = percolate_space(bn, space, strict_percolation=False)
+    perc_bn = percolate_network(bn, perc_space)
+
+    perc_bnet = perc_bn.to_bnet()
+
+    # remove constant nodes from the bnet
+    clean_bnet = ""
+    for line in perc_bnet.split("\n"):
+        if line.strip() == "":
+            continue
+        node = line.split(",")[0]
+        function = line.split(",")[1].strip()
+        if function == "("+node+" | !"+node+")":
+            continue
+        elif function == "("+node+" & !"+node+")":
+            continue
+        else:
+            clean_bnet += line + "\n"
+
+    clean_bn = BooleanNetwork.from_bnet(clean_bnet)
+
+    return clean_bn
+
+
+def find_source_nodes(network: BooleanNetwork | DiGraph) -> list[str]:
+    
+    if isinstance(network, BooleanNetwork):
+        bn = network
+        petri_net = network_to_petrinet(network)
+    else:
+        bn = None
+        petri_net = network
+
+    assert isinstance(petri_net, DiGraph)
+
+    if bn is None:
+        variables = extract_variable_names(petri_net)
+    else:
+        variables = [bn.get_variable_name(v) for v in bn.variables()]
+
+    # Source node is a node that has no transitions in the PN encoding
+    # (i.e. it's value cannot change).
+    source_set = set(variables)
+    for _, change_var in petri_net.nodes(data="change"):  # type: ignore
+        if change_var in source_set:
+            source_set.remove(change_var)  # type: ignore[reportUnknownArgumentType] # noqa
+    source_nodes: list[str] = sorted(source_set)
+
+    return source_nodes
+
+# di = infer_signed_interaction_graph(perc_bn)
+
+# scc_list = [x for x in nx.strongly_connected_components(di)]
+
+# source_scc_list = []
+# for scc in scc_list:
+#     source = True
+#     for node in scc:
+#         for reg in di.predecessors(node):
+#             if reg not in scc:
+#                 source = False
+#                 break
+#         if not source:
+#             break
+#     if source:
+#         source_scc_list.append(scc)
+
+# print(source_scc_list)
+
+# print(perc_bnet)
+
+# est_size = 1
+# est_depth = 0
+# est_min = 1
+
+# for source_scc in source_scc_list:
+#     print("source_scc:", source_scc)
+#     scc_bnet = "targets,factors\n"
+#     for line in perc_bnet.split("\n"):
+#         for node in source_scc:
+#             if line.startswith(node+","):
+#                 scc_bnet += line + "\n"
+
+#     scc_bn = BooleanNetwork.from_bnet(scc_bnet)
+
+#     print(scc_bn.to_bnet())
+#     scc_bn = scc_bn.infer_regulatory_graph()
+
+#     for var in scc_bn.implicit_parameters():
+#         scc_bn.set_update_function(var, "true")
+
+#     scc_bn = scc_bn.infer_regulatory_graph()
+
+
+#     # Compute the succession diagram.
+#     sd = SuccessionDiagram(scc_bn)
+#     fully_expanded = sd.expand_bfs(bfs_level_limit=DEPTH_LIMIT, size_limit=NODE_LIMIT)
+#     assert fully_expanded
+
+#     print(f"SD size, {len(sd)}")
+#     print(f"SD depth, {sd.depth()} ")
+#     print(f"minimal trapspaces, {len(sd.minimal_trap_spaces())}")
+
+#     est_size *= len(sd)
+#     est_depth += sd.depth()
+#     est_min *= len(sd.minimal_trap_spaces())
+
+# print(f"{est_size=}")
+# print(f"{est_depth=}")
+# print(f"{est_min=}")
+
+# log = open(LOG_LOCATION, "a")
+# log.write(sys.argv[1].split("/")[-1] + ",")  # model name
+# log.write(str(bn.num_vars()) + ",")  # network size
+# log.write(str(len(source_scc_list)) + ",")  # number of source_scc
+# log.write(str(len(scc_list)) + ",") # number of scc
+# log.write(str(est_size) + ",") # estimated SD size
+# log.write(str(est_depth) + ",") # estimated SD depth
+# log.write(str(est_min) + "\n") # estimated number of attractors
diff --git a/nfvsmotifs/_sd_algorithms/test.bnet b/nfvsmotifs/_sd_algorithms/test.bnet
new file mode 100644
index 00000000..432c8857
--- /dev/null
+++ b/nfvsmotifs/_sd_algorithms/test.bnet
@@ -0,0 +1,9 @@
+targets,factors
+constant1_1, (constant1_1 | !constant1_1)
+constant1_0, (constant1_0 & !constant1_0)
+constant2_1, true
+constant2_0, false
+source, source
+oscillator, !oscillator
+source_after_perc, source_after_perc & constant1_1
+after_perc_0, after_perc_0 & constant1_0
\ No newline at end of file
diff --git a/nfvsmotifs/_sd_algorithms/test.py b/nfvsmotifs/_sd_algorithms/test.py
new file mode 100644
index 00000000..df32215f
--- /dev/null
+++ b/nfvsmotifs/_sd_algorithms/test.py
@@ -0,0 +1,25 @@
+from expand_source_SCCs import *
+
+
+bn = BooleanNetwork.from_file("nfvsmotifs/_sd_algorithms/test.bnet")
+
+source_nodes = find_source_nodes(bn)
+
+print(source_nodes)
+
+perc_space, _ = percolate_space(bn, {}, strict_percolation=False)
+perc_bn = percolate_network(bn, perc_space)
+
+source_nodes = find_source_nodes(perc_bn)
+
+print(source_nodes)
+
+bin_values_list = it.product(range(2), repeat=len(source_nodes)) 
+for bin_values in bin_values_list:
+    source_comb = dict(zip(source_nodes, bin_values))
+    print(source_comb)
+
+    sub_space = source_comb
+    sub_space.update(perc_space)
+
+    print(sub_space)
\ No newline at end of file