diff --git a/.gitignore b/.gitignore
index e69de29bb2d1d6434b8b29ae775ad8c2e48c5391..264dacab5a7aa25c1c26c6c3b20d48d637fe4b49 100644
--- a/.gitignore
+++ b/.gitignore
@@ -0,0 +1 @@
+*__pycache__
\ No newline at end of file
diff --git a/__init__.py b/__init__.py
new file mode 100644
index 0000000000000000000000000000000000000000..e69de29bb2d1d6434b8b29ae775ad8c2e48c5391
diff --git a/__main__.py b/__main__.py
index e69de29bb2d1d6434b8b29ae775ad8c2e48c5391..86d59a274a0b8d734ecb3c3f16b446e8ec19ce63 100644
--- a/__main__.py
+++ b/__main__.py
@@ -0,0 +1,4 @@
+import elements
+import graphics
+
+print("Hi World!")
diff --git a/elements/__init__.py b/elements/__init__.py
index 9664db059251e7c9e9a2e29007f3fe619d4c6b51..fa0c9bc11702417e6c46868e3bbf31e908fdb3b8 100644
--- a/elements/__init__.py
+++ b/elements/__init__.py
@@ -1,2 +1,4 @@
 import numpy as np
 import cmath
+
+from .main import *
diff --git a/elements/main.py b/elements/main.py
index 03a98168c6b2b9634757a19428a1681b28ec55f4..2026c2b4875b5ed75f202040b8b47496a1af75bd 100644
--- a/elements/main.py
+++ b/elements/main.py
@@ -1,3 +1,5 @@
+import numpy as np
+
 ### ------ Special elements ------
 class Source:
     def __init__(self, initial_vector=np.array([1., 0.+0j])): ## if no input state given, starts a |0>
@@ -13,11 +15,12 @@ class Screen:
         self.previous = previous
 
     def show(self):
-        previous_component, previous_component_output_side = previous
+        previous_component, previous_component_output_side = self.previous
         print(previous_component.out(previous_component_output_side))
 
     def out(self):
-        return previous_component.out(previous_component_output_site)
+        previous_component, previous_component_output_side = self.previous
+        return previous_component.out(previous_component_output_side)
 
 
 
@@ -28,19 +31,21 @@ class Element:
         self.next = None
 
 class Plate(Element):
-    def __init__(self, jones_matrix = np.eye((2, 2), dtype='complex')):
+    def __init__(self, previous, jones_matrix = np.eye(2, dtype='complex')):
+        Element.__init__(self, previous)
         self.jones_matrix = jones_matrix
         self.output_vector = None
 
     def out(self, side):
         previous_element = self.previous[0]
         previous_element_output_side = self.previous[1]
-        self.output_vector = self.jones_matrix @ previous_element(previous_element_output_side) # matrix-vector product : jones matrix times state vector given by the out(side) method of the previous component
+        self.output_vector = self.jones_matrix @ previous_element.out(previous_element_output_side) # matrix-vector product : jones matrix times state vector given by the out(side) method of the previous component
         return self.output_vector
 
 class BeamSplitter(Element):
     """matrix is a 4x4 complex ndarray, two first dimensions regard left input, two next are right. So it's blockwise defined."""
-    def __init__(self, matrix = np.eye((4, 4), dtype='complex')):
+    def __init__(self, previous, matrix = np.eye(4, dtype='complex')):
+        Element.__init__(self, previous)
         self.matrix = matrix
         self.output_vector = None