Update tutorials (#463)

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Co-authored-by: Dario Coscia <93731561+dario-coscia@users.noreply.github.com>

tutorials/tutorial6/tutorial.py

@@ -26,7 +26,7 @@ if IN_COLAB:
   get_ipython().system('pip install "pina-mathlab"')
 
 import matplotlib.pyplot as plt
-plt.style.use('tableau-colorblind10')
+
 from pina.domain import EllipsoidDomain, Difference, CartesianDomain, Union, SimplexDomain, DomainInterface
 from pina.label_tensor import LabelTensor
 
@@ -175,7 +175,6 @@ plot_scatter(ax, c_e_nb_d_points, 'Difference')
 
 import torch
 from pina import LabelTensor
-import random
 
 
 # Next, we will create the `Heart(DomainInterface)` class and initialize it.
@@ -191,12 +190,6 @@ class Heart(DomainInterface):
         
 
 
-# In[ ]:
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-
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 # Because the `DomainInterface` class we are inheriting from requires both a `sample` method and `is_inside` method, we will create them and just add in "pass" for the moment. We also observe that the methods `sample_modes` and `variables` of the `DomainInterface` class are initialized as `abstractmethod`, so we need to redefine them both in the subclass `Heart` .
 
 # In[13]: