|:: focus on node $n :focus: $|
    :: ensure node $n exists
    :focus: $n
|:: focus on node $n|
    :: ensure node $n exists
    :focus: $n

||:nodes: root horizontal
|:: create a node under root :unique ID: $x?|
    :: go to the next unique ID
    :edges: root $x
    :nodes: $x horizontal
|:: create a node under $n :unique ID: $x?|
    :: ensure node $n exists
    :: go to the next unique ID
    :edges: $n $x
    :nodes: $x horizontal

|:: set node $n to use a $s split :nodes: $n $|
    :nodes: $n $s
    :: reset nodes
|:: set node $n to use a $s split :not found: $n|
    :: error :message: $n is not a node
|:: set node $n to use a $s split?|
    :: find node $n

|:: find node $n :nodes: $n $?|
|:: find node $n? :nodes: $x $y|
    :checked nodes: $x $y
|:: find node $n|
    :not found: $n
    :: reset nodes

|:: ensure node $n exists :not found: $n|
    :: error :message: $n is not a node
|:: ensure node $n exists :nodes: $n $?|
    :: reset nodes
|:: ensure node $n exists?|
    :: find node $n

|:: reset nodes? :checked nodes: $x $y|
    :nodes: $x $y
|:: reset nodes|

||:unique ID: 0
|:: go to the next unique ID :@math: $x|
    :unique ID: $x
|:: go to the next unique ID? :unique ID: $n|
    :@math: add $n 1

||:: create a node under root
  :: create a node under 0
  :: create a node under 0
  :: create a node under 1
  :: create a node under 3
  :: set node 0 to use a vertical split
  :: set node 3 to use a vertical split