[[1, "a"], [2, "a"], [3, "a"]]
[[1, "b"], [2, "a"], [3, "a"]]
[[1, "a"], [2, "b"], [3, "a"]]
[[1, "b"], [2, "b"], [3, "a"]]
[[1, "a"], [2, "a"], [3, "b"]]
[[1, "b"], [2, "a"], [3, "b"]]
[[1, "a"], [2, "b"], [3, "b"]]
[[1, "b"], [2, "b"], [3, "b"]]