solo para principiantes ..-_-..
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---------------0---- x2
-------------2------
-----0-0---4--------
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--------------------------
---------------0--4--2--0- x2
-------------2------------
-----0-0---4--------------
-------------------------------
-------------------------------
------------------------------- x2
--------2-3-4-------4----------
-0-0-4------------4---4--------
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-------------------------------
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-00--00--22--22----------------
---00--00--22--22--------------