diff --git a/src/envs/circular.jl b/src/envs/circular.jl
index e3e91a4..afac476 100644
--- a/src/envs/circular.jl
+++ b/src/envs/circular.jl
@@ -140,12 +140,13 @@ function POMDPs.observations(pomdp::CircularMaze)
     # NOTE: In JuliaPOMDPs, an observation space is NOT the set of possible distributions, but rather union of the support of all possible observations
     corridors = 1:pomdp.n_corridors  # from CMAZE_SENSE_CORRIDOR
     perms = permutations(pomdp.probabilities)
-    space = chain(corridors, perms)  # generator
+    space = Iterators.flatten(corridors, perms)  # generator
     return space
 end
 
 # TODO: maybe implement POMDPs.obsindex
 
+# TODO: confirm that transitions are non-Deterministic
 function POMDPs.transition(pomdp::CircularMaze, s::CircularMazeState, a::Integer)
     @assert a in actions(pomdp) "Unrecognized action $a"
     if a == CMAZE_DECLARE_GOAL
diff --git a/src/updaters/kalman.jl b/src/updaters/kalman.jl
new file mode 100644
index 0000000..7ae2695
--- /dev/null
+++ b/src/updaters/kalman.jl
@@ -0,0 +1,12 @@
+import POMDPs
+
+struct HistoryUpdater <: POMDPs.Updater end
+
+POMDPs.initialize_belief(up::HistoryUpdater, d) = Any[d]
+
+function POMDPs.update(up::HistoryUpdater, b, a, o)
+    bp = copy(b)
+    push!(bp, a)
+    push!(bp, o)
+    return bp
+end
\ No newline at end of file
diff --git a/test/circular_tests.jl b/test/circular_tests.jl
index 1c7793f..c94059f 100644
--- a/test/circular_tests.jl
+++ b/test/circular_tests.jl
@@ -1,5 +1,5 @@
 let
-    pomdp = CircularMaze()
+    pomdp = CircularMaze(2, 5, 0.99)
 
     policy = RandomPolicy(pomdp, rng=MersenneTwister(2))
     sim = RolloutSimulator(rng=MersenneTwister(3), max_steps=100)