isSearchTree (Node 5 (Node 3 Nil Nil) (Node 7 Nil Nil)) == True
isSearchTree (Node 5 (Node 5 Nil Nil) (Node 7 Nil Nil)) == False

makeSearchTree (Node 3 (Node 5 Nil Nil) (Node 7 Nil Nil)) == (Node 5 (Node 3 Nil Nil) (Node 7 Nil Nil))
makeSearchTree (Node 3 (Node 5 Nil Nil) (Node 7 Nil Nil)) == (Node 7 (Node 3 Nil (Node 5 Nil Nil)) Nil)
-- waeren zwei Resultate, die zulaessige Implementierungen von makeSearchTree liefern duerften.

layerToSearchTree (Node 1 (Node 3 (Node 5 Nil Nil) (Node 7 Nil Nil)) (Node 9 (Node 11 Nil Nil) Nil)) 1 == (Node 9 (Node 3 Nil Nil) Nil)
layerToSearchTree (Node 1 (Node 3 (Node 5 Nil Nil) (Node 7 Nil Nil)) (Node 9 (Node 11 Nil Nil) Nil)) 2 == (Node 7 (Node 5 Nil Nil) (Node 11 Nil Nil))

maxSearchTreeSum (Node 1 (Node 5 (Node 3 Nil Nil) (Node 7 Nil Nil)) Nil) == 15
maxSearchTreeSum (Node 1 (Node 5 (Node 42 Nil Nil) Nil) (Node 2 (Node 1 Nil Nil) (Node 6 Nil Nil))) == 42