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class Albero:
    def __init__(self,val):
        self.val = val
        self.sx = None
        self.dx = None



a = Albero(4)
b = Albero(1)
c = Albero(2)
d = Albero(6)

a.dx = d
a.sx = b
b.dx = c


def inorder(a,l):

    if a.sx != None:
        inorder(a.sx,l)

    l.append(a.val)

    if a.dx != None:
        inorder(a.dx,l)



def preorder(a):

    print(a.val)

    if a.sx != None:
        inorder(a.sx)


    if a.dx != None:
        inorder(a.dx)

def postorder(a):

    if a.sx != None:
        inorder(a.sx)


    if a.dx != None:
        inorder(a.dx)

    print(a.val)

l = []
inorder(a,l)