diff --git a/.gitignore b/.gitignore
index f1c6544..d77c715 100644
--- a/.gitignore
+++ b/.gitignore
@@ -105,3 +105,6 @@ venv.bak/
 
 # data files
 referencePathways/reactome/*.gOut
+
+# output files
+*.sif
\ No newline at end of file
diff --git a/graph5_flow1_c1.0.sif b/graph5_flow1_c1.0.sif
deleted file mode 100644
index 684842d..0000000
--- a/graph5_flow1_c1.0.sif
+++ /dev/null
@@ -1,2 +0,0 @@
-B	A
-C	B
diff --git a/graphs/graph5/edges.txt b/graphs/graph5/edges.txt
index bb629d3..2ca040c 100644
--- a/graphs/graph5/edges.txt
+++ b/graphs/graph5/edges.txt
@@ -1,9 +1,12 @@
-A	B	0.98
-B	C	0.77
-A	D	0.12
-C	D	0.89
-C	E	0.59
-C	F	0.50
-F	G	0.76
-G	H	0.92
-G	I	0.66
+A	B	0.98	U
+B	C	0.77	U
+A	D	0.12	U
+A	D	0.12	D
+C	D	0.89	U
+C	E	0.59	U
+A	D	0.12	D
+C	F	0.50	U
+F	G	0.76	U
+G	H	0.92	U
+G	I	0.66	U
+B	C	0.77	U
\ No newline at end of file
diff --git a/graphs/graph_dir_col/edges.txt b/graphs/graph_dir_col/edges.txt
deleted file mode 100644
index 3ac04d7..0000000
--- a/graphs/graph_dir_col/edges.txt
+++ /dev/null
@@ -1,9 +0,0 @@
-A	B	0.98	U
-B	C	0.77	U
-A	D	0.12	D
-C	D	0.89	U
-C	E	0.59	U
-C	F	0.50	U
-F	G	0.76	U
-G	H	0.92	U
-G	I	0.66	U
diff --git a/graphs/graph_dir_col/sources.txt b/graphs/graph_dir_col/sources.txt
deleted file mode 100644
index 8c7e5a6..0000000
--- a/graphs/graph_dir_col/sources.txt
+++ /dev/null
@@ -1 +0,0 @@
-A
\ No newline at end of file
diff --git a/graphs/graph_dir_col/targets.txt b/graphs/graph_dir_col/targets.txt
deleted file mode 100644
index 2c29ca5..0000000
--- a/graphs/graph_dir_col/targets.txt
+++ /dev/null
@@ -1,4 +0,0 @@
-C
-D
-H
-I
\ No newline at end of file
diff --git a/minCostFlow.py b/minCostFlow.py
index 5e2fe56..9f2b2ec 100644
--- a/minCostFlow.py
+++ b/minCostFlow.py
@@ -47,17 +47,19 @@ def construct_digraph(edges_file, cap):
             w = int((1-(float(tokens[2])))*100)
             d = tokens[3]
 
-            if d == "U":
+            # TODO: is it better to overwrite the edges or just to throw an error
+            if (node1, node2) in edges_dict:
+                raise KeyError(f"Failed to add the edge ({node1}, {node2}) with weight '{tokens[2]}' and directionality '{d}'. This edge conflicts with an existing '{edges_dict[(node1, node2)]}' edge in the graph.")
+            elif d == "U":
                 edges_dict[(node1, node2)] = "U"
                 edges_dict[(node2, node1)] = "U"
                 G.add_arc_with_capacity_and_unit_cost(idDict[node1],idDict[node2], default_capacity, int(w))
                 G.add_arc_with_capacity_and_unit_cost(idDict[node2],idDict[node1], default_capacity, int(w))
-
             elif d == "D":
                 edges_dict[(node1, node2)] = "D"
                 G.add_arc_with_capacity_and_unit_cost(idDict[node1],idDict[node2], default_capacity, int(w))
             else: 
-                raise ValueError (f"d = {d}")
+                raise ValueError (f"Cannot add egdge: d = {d}")
 
     idDict["maxID"] = curID
     return G,idDict