将嵌套地图展平为行

Question

在clojure中，我怎样才能像这样转换嵌套地图：

{"1" {"1.1" {}
      "1.2" {}}
 "2" {"2.1" {}
      "2.2" {}
      "2.3" {}}}

进入这个：

[["1" "1.1"]
 ["1" "1.2"]
 ["2" "2.1"]
 ["2" "2.2"]
 ["2" "2.3"]]

如果嵌套不受限制