diff --git a/level5/expanding-nebula/solution.py b/level5/expanding-nebula/solution.py
index deda8db..f2b2521 100644
--- a/level5/expanding-nebula/solution.py
+++ b/level5/expanding-nebula/solution.py
@@ -6,9 +6,12 @@ def solution(g):
     #print grid
     height, width = grid.shape
     #print height, width
+    
+    prev_cases = {i:1 for i in generate_prev_cases(grid[:,0])}
+    #prev_cases = {i:1 for i in range(2**(len(column)+1))}
+    #print prev_cases
 
     memo = {}
-    prev_cases = {i:1 for i in range(2**(height+1))}
     #for i in range(2**(height+1)):
     #    prev_cases[i] = 1
     #    memo[i] = {j:calculate_c_column(i, j, height) for j in range(2**(height+1))}
@@ -33,6 +36,24 @@ def solution(g):
         prev_cases = cases
     return sum(prev_cases.values())
 
+def generate_prev_cases(column):
+    #print column
+    if len(column) == 0:
+        yield 0
+        yield 1
+    else:
+        for v in generate_prev_cases(column[:-1]):
+            #print 'v', v
+            if column[len(column)-1] and v&1 == 1:
+                yield v<<1|0
+            else:
+                yield v<<1|0
+                yield v<<1|1
+
+#for t in [[True], [False], [True, True], [True, False], [False, True], [False, False]]:
+#    print 'run', t, list(generate_prev_cases(t))
+#exit(0)
+
 def print_grid(g):
     for row in g:
         line = ""