def __setitem__(self, key, value):
if key == <NUM_LIT:0>:<EOL><INDENT>self.left = value<EOL><DEDENT>else:<EOL><INDENT>self.right = value<EOL><DEDENT>
N.__setitem__(key, value) <==> x[key]=value, where key is 0 (left) or 1 (right).