diff --git a/csa/elementary.py b/csa/elementary.py
index 4d848b8..a08c785 100644
--- a/csa/elementary.py
+++ b/csa/elementary.py
@@ -28,10 +28,26 @@
 
 # Connection-Set constructor
 #
-def cset (mask, *valueSets):
+def cset(mask, *valueSets):
+    """
+    Construct a ConnectionSet from a mask and optional value sets.
+
+    Parameters
+    ----------
+    mask : Mask
+        A mask defining the connectivity pattern.
+    *valueSets : ValueSet
+        Optional value sets associated with the connection set.
+
+    Returns
+    -------
+    ConnectionSet or Mask
+        If value sets are provided, returns a ConnectionSet object.
+        Otherwise, returns the mask unchanged.
+    """
     if valueSets:
-        c = _cs.ExplicitCSet (mask, *valueSets)
-        return _cs.ConnectionSet (c)
+        c = _cs.ExplicitCSet(mask, *valueSets)
+        return _cs.ConnectionSet(c)
     else:
         return mask
 
@@ -63,15 +79,45 @@ def vset (obj):
 
 # Intervals
 #
-def ival (beg, end):
-    return _iset.IntervalSet ((beg, end))
+def ival(beg, end):
+    """
+    Create an IntervalSet representing a closed interval.
+
+    Parameters
+    ----------
+    beg : int
+        Beginning of the interval.
+    end : int
+        End of the interval.
+
+    Returns
+    -------
+    IntervalSet
+        An interval set containing the specified range.
+    """
+    return _iset.IntervalSet((beg, end))
 
 N = _iset.N
 
 # Cartesian product
 #
-def cross (set0, set1):
-    return _cs.intervalSetMask (set0, set1)
+def cross(set0, set1):
+    """
+    Compute the Cartesian product mask between two interval sets.
+
+    Parameters
+    ----------
+    set0 : IntervalSet
+        The first interval set.
+    set1 : IntervalSet
+        The second interval set.
+
+    Returns
+    -------
+    Mask
+        A mask representing the Cartesian product of the two sets.
+    """
+    return _cs.intervalSetMask(set0, set1)
 
 # Elementary masks
 #
diff --git a/csa/plot.py b/csa/plot.py
index dd2fecc..1f55ae9 100644
--- a/csa/plot.py
+++ b/csa/plot.py
@@ -43,7 +43,7 @@ def show (cset, N0 = 30, N1 = None):
     a = _numpy.zeros ((N0, N1))
     for (i, j) in elementary.cross (range (N0), range (N1)) * cset:
         a[i,j] += 1.0
-    _plt.imshow (a, interpolation='nearest', vmin = 0.0, vmax = 1.0)
+    _plt.imshow(a, interpolation='nearest', vmin=0.0, vmax=1.0, cmap=_plt.cm.gray)
     _plt.show ()
 
 def gplotsel2d (g, cset, source = elementary.N, target = elementary.N, N0 = 900, N1 = None, value = None, range=[], lines = True):