diff --git a/examples/rectangle.jl b/examples/rectangle.jl
index 4b89566..c0d3dc6 100644
--- a/examples/rectangle.jl
+++ b/examples/rectangle.jl
@@ -61,8 +61,20 @@ C = Pl * F # coefficient 3-array in tensor basis
 
 
 c = DiagTrav(C) # arrange by total degree
-# ret = 0.0
-# for n=0:N-1, k=0:n, j=0:n-k
-#     ret += c[Block(n+1)[k+1]] * P[0.1,n-k-j + 1] * P[0.2,k + 1] * P[0.3,j + 1]
-# end
-# @test ret ≈ f(0.1,0.2)
\ No newline at end of file
+
+function check_DiagTrav3D(c,P)
+    ret = 0.0
+    for n=1:N
+        iter=1
+        for i=reverse(1:n)
+            k=0
+            for j=reverse(1:(n-i+1)) 
+                k+=1
+                ret += c[Block(n)[iter]] * P[0.1,i] * P[0.2,j] * P[0.3,k]
+                iter+=1
+            end
+        end
+    end
+    ret
+end
+@test check_DiagTrav3D(c,P) ≈ f(0.1,0.2,0.3)
\ No newline at end of file