diff --git a/pytriqs/gf/local/CMakeLists.txt b/pytriqs/gf/local/CMakeLists.txt
index 20cdf46a..1387a7ff 100644
--- a/pytriqs/gf/local/CMakeLists.txt
+++ b/pytriqs/gf/local/CMakeLists.txt
@@ -9,12 +9,12 @@ SET(PYTHON_SOURCES
   ${CMAKE_CURRENT_SOURCE_DIR}/_gf_legendre.py
   ${CMAKE_CURRENT_SOURCE_DIR}/_gf_refreq.py
   ${CMAKE_CURRENT_SOURCE_DIR}/_gf_retime.py
-  #${CMAKE_CURRENT_SOURCE_DIR}/gf_two_real_times.py
   ${CMAKE_CURRENT_SOURCE_DIR}/_gf_plot.py
   ${CMAKE_CURRENT_SOURCE_DIR}/_gf_common.py
   ${CMAKE_CURRENT_SOURCE_DIR}/inverse.py
   ${CMAKE_CURRENT_SOURCE_DIR}/lazy_expressions.py
   ${CMAKE_CURRENT_SOURCE_DIR}/tools.py
+  ${CMAKE_CURRENT_SOURCE_DIR}/functions.py
 )
 
 # Install python sources
diff --git a/pytriqs/gf/local/__init__.py b/pytriqs/gf/local/__init__.py
index 70c684d6..2092df63 100644
--- a/pytriqs/gf/local/__init__.py
+++ b/pytriqs/gf/local/__init__.py
@@ -29,24 +29,16 @@ It is imported with the command::
 from gf import *
 
 from inverse import inverse
-#from gf_imfreq import GfImFreq
-#from gf_imtime import GfImTime
-#from gf_refreq import GfReFreq
-#from gf_retime import GfReTime
-#from gf_two_real_times import GfTwoRealTime
-#from gf_legendre import GfLegendre
 from block_gf import BlockGf
 from descriptors import Omega, iOmega_n, SemiCircular, Wilson, Fourier, InverseFourier, LegendreToMatsubara, MatsubaraToLegendre
+from functions import delta
 
-#__all__ = ['TailGf','GfImFreq','MeshImFreq']
-
-__all__ = ['Omega','iOmega_n','SemiCircular','Wilson','Fourier','InverseFourier','LegendreToMatsubara','MatsubaraToLegendre','lazy_expressions','TailGf',
+__all__ = ['Omega','iOmega_n','SemiCircular','Wilson','Fourier','InverseFourier','LegendreToMatsubara','MatsubaraToLegendre',
+           'lazy_expressions','TailGf',
            'GfImFreq','MeshImFreq',
            'GfImTime', 'MeshImTime',
            'GfReFreq', 'MeshReFreq',
            'GfReTime', 'MeshReTime',
            'make_gf_from_inverse_fourier',
-           'BlockGf','inverse'] #,'GfTwoRealTime']
-
-#__all__ = ['Omega','iOmega_n','SemiCircular','Wilson','Fourier','InverseFourier','LegendreToMatsubara','MatsubaraToLegendre','lazy_expressions','TailGf','GfImFreq','GfImTime','GfReFreq','GfReTime','GfLegendre','BlockGf','inverse'] #,'GfTwoRealTime']
-
+           'BlockGf','inverse',
+           'delta']
diff --git a/pytriqs/gf/local/block_gf.py b/pytriqs/gf/local/block_gf.py
index 50964ebb..be4fcc30 100644
--- a/pytriqs/gf/local/block_gf.py
+++ b/pytriqs/gf/local/block_gf.py
@@ -364,11 +364,6 @@ class BlockGf(object):
        self.__check_attr("invert")
        for i,g in self : g.invert()
 
-    def delta(self) :
-       """Compute delta from G0"""
-       self.__check_attr("delta")
-       return self.__class__( name_block_generator = [ (n, g.delta()) for n,g in self], make_copies=False)
-
     def transpose(self):
        """Transpose of the BlockGf"""
        self.__check_attr("transpose")
diff --git a/pytriqs/gf/local/functions.py b/pytriqs/gf/local/functions.py
new file mode 100644
index 00000000..303ac87c
--- /dev/null
+++ b/pytriqs/gf/local/functions.py
@@ -0,0 +1,17 @@
+from inverse import inverse
+from block_gf import BlockGf
+from gf import GfImFreq
+from descriptor_base import A_Omega_Plus_B
+
+def delta(g) :
+    """Compute delta from G0"""
+    if type(g) == BlockGf:
+    	return BlockGf(name_block_generator = [ (n, delta(g0)) for n,g0 in g], make_copies=False)
+    elif type(g) == GfImFreq:
+    	g0_iw_inv = inverse(g)
+    	delta_iw = g0_iw_inv.copy()
+    	delta_iw <<= A_Omega_Plus_B(g0_iw_inv.tail[-1], g0_iw_inv.tail[0])
+    	delta_iw -= g0_iw_inv
+        return delta_iw
+    else:
+        raise TypeError, "No function delta for g0 object of type %s"%type(g)