diff --git a/src/Mono.cs b/src/Mono.cs
index 13a01fe..fca97db 100644
--- a/src/Mono.cs
+++ b/src/Mono.cs
@@ -215,4 +215,15 @@ static class Mono
         new XYZi(0, 0, -1), // fwd
         new XYZi(0, 0, +1), // back
     };
+    static readonly XYZi[] corners = new XYZi[]
+    {
+        new XYZi(-1, -1, -1),
+        new XYZi(-1, -1, +1),
+        new XYZi(-1, +1, -1),
+        new XYZi(-1, +1, +1),
+        new XYZi(+1, -1, -1),
+        new XYZi(+1, -1, +1),
+        new XYZi(+1, +1, -1),
+        new XYZi(+1, +1, +1)
+    };
 }