t = tree(10 50 10)
x = 10
y = left ( right (tree(50 10 20)))
y = + x y ++
z = y ++ --
print y
while (| <= x 20 > y 10)
{
 x = - + x y z
}
/* this
is 
a demo
*/
y= 0x7777777777777777777777777