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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def surface(n_x=20,n_y=20):
 	""" 	Returns a DataFrame with the required format for 	a surface plot 	Parameters: 		n_x : int 			Number of points along the X axis 		n_y : int 			Number of points along the Y axis 	"""
	
	x=[float(np.random.randint(0,100))]
	for i in range(n_x):
		x.append(x[:1][0]+np.random.randn()*np.random.randint(1,10))
	df=pd.DataFrame(x)
	for i in range(n_y):
		df[i+1]=df[i].map(lambda x:x+np.random.randn()*np.random.randint(1,10))
	return df