diff --git a/python/spot/impl.i b/python/spot/impl.i
index a279d5d96..2a1db01ff 100644
--- a/python/spot/impl.i
+++ b/python/spot/impl.i
@@ -495,6 +495,60 @@ namespace std {
   }
 }
 
+%extend std::set<spot::formula> {
+  std::string __str__()
+  {
+    std::ostringstream s;
+    s << "{";
+    bool comma = false;
+    for (auto& i: *self)
+      {
+        if (comma)
+          s << ", ";
+        else
+          comma = true;
+        spot::print_psl(s, i);
+      }
+    s << "}";
+    return s.str();
+  }
+
+  std::string __repr__()
+  {
+    std::ostringstream s;
+    s << "{";
+    bool comma = false;
+    for (auto& i: *self)
+      {
+        if (comma)
+          s << ", ";
+        else
+          comma = true;
+        spot::print_psl(s, i);
+      }
+    s << "}";
+    return s.str();
+  }
+
+  std::string _repr_latex_()
+  {
+    std::ostringstream s;
+    s << "$\\{";
+    bool comma = false;
+    for (auto& i: *self)
+      {
+        if (comma)
+          s << ", ";
+        else
+          comma = true;
+        spot::print_sclatex_psl(s, i);
+      }
+    s << "\\}$";
+    return s.str();
+  }
+
+}
+
 %exception spot::formula::__getitem__ {
   try {
     $action
diff --git a/python/spot/ltsmin.i b/python/spot/ltsmin.i
index 03e490de2..1483df950 100644
--- a/python/spot/ltsmin.i
+++ b/python/spot/ltsmin.i
@@ -57,10 +57,6 @@ using namespace spot;
   }
 }
 
-namespace std {
-  %template(atomic_prop_set) set<spot::formula>;
-}
-
 %rename(model) spot::ltsmin_model;
 %rename(kripke_raw) spot::ltsmin_model::kripke;
 %include <spot/ltsmin/ltsmin.hh>
diff --git a/tests/python/ltsmin.ipynb b/tests/python/ltsmin.ipynb
index 069a0c5e1..c8e84e95c 100644
--- a/tests/python/ltsmin.ipynb
+++ b/tests/python/ltsmin.ipynb
@@ -18,7 +18,7 @@
    "version": "3.5.1"
   },
   "name": "",
-  "signature": "sha256:d1444ee3c1e56aaa453ac171d129f0ba4486e1e194debc51965d45429a844334"
+  "signature": "sha256:c71f218a80ffc2fb08377daa20d703d7c421278e48d625c4f9fca8ff8f59d80a"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -447,7 +447,7 @@
         "</svg>\n"
        ],
        "text": [
-        "<spot.impl.kripke; proxy of <Swig Object of type 'std::shared_ptr< spot::kripke > *' at 0x7f7b280d08a0> >"
+        "<spot.impl.kripke; proxy of <Swig Object of type 'std::shared_ptr< spot::kripke > *' at 0x7f1de22e1870> >"
        ]
       }
      ],
@@ -726,7 +726,7 @@
         "</svg>"
        ],
        "text": [
-        "<IPython.core.display.SVG at 0x7f7b280dd630>"
+        "<IPython.core.display.SVG at 0x7f1de228ae80>"
        ]
       }
      ],
@@ -1082,7 +1082,7 @@
         "</svg>"
        ],
        "text": [
-        "<IPython.core.display.SVG at 0x7f7b110b9c50>"
+        "<IPython.core.display.SVG at 0x7f1de228ab38>"
        ]
       }
      ],
@@ -1152,7 +1152,7 @@
         "</svg>\n"
        ],
        "text": [
-        "<spot.impl.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f7b2fcf8090> >"
+        "<spot.impl.twa_graph; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_graph > *' at 0x7f1dd5f6a630> >"
        ]
       }
      ],
@@ -1314,12 +1314,92 @@
         "</svg>\n"
        ],
        "text": [
-        "<spot.impl.twa_product; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_product > *' at 0x7f7b280d08d0> >"
+        "<spot.impl.twa_product; proxy of <Swig Object of type 'std::shared_ptr< spot::twa_product > *' at 0x7f1de22e17e0> >"
        ]
       }
      ],
      "prompt_number": 13
     },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "If we want to create a `model_check` function that takes a model and formula, we need to get the list of atomic propositions used in the formula using `atomic_prop_collect()`.  This returns an `atomic_prop_set`:"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "a = spot.atomic_prop_collect(spot.formula('\"a < 2\" W \"b == 1\"'))\n",
+      "dir(a)"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "metadata": {},
+       "output_type": "pyout",
+       "prompt_number": 17,
+       "text": [
+        "['__bool__',\n",
+        " '__class__',\n",
+        " '__contains__',\n",
+        " '__delattr__',\n",
+        " '__dict__',\n",
+        " '__dir__',\n",
+        " '__doc__',\n",
+        " '__eq__',\n",
+        " '__format__',\n",
+        " '__ge__',\n",
+        " '__getattribute__',\n",
+        " '__getitem__',\n",
+        " '__gt__',\n",
+        " '__hash__',\n",
+        " '__init__',\n",
+        " '__iter__',\n",
+        " '__le__',\n",
+        " '__len__',\n",
+        " '__lt__',\n",
+        " '__module__',\n",
+        " '__ne__',\n",
+        " '__new__',\n",
+        " '__nonzero__',\n",
+        " '__reduce__',\n",
+        " '__reduce_ex__',\n",
+        " '__repr__',\n",
+        " '__setattr__',\n",
+        " '__sizeof__',\n",
+        " '__str__',\n",
+        " '__subclasshook__',\n",
+        " '__swig_destroy__',\n",
+        " '__weakref__',\n",
+        " 'add',\n",
+        " 'append',\n",
+        " 'begin',\n",
+        " 'clear',\n",
+        " 'count',\n",
+        " 'discard',\n",
+        " 'empty',\n",
+        " 'end',\n",
+        " 'equal_range',\n",
+        " 'erase',\n",
+        " 'find',\n",
+        " 'insert',\n",
+        " 'iterator',\n",
+        " 'lower_bound',\n",
+        " 'rbegin',\n",
+        " 'rend',\n",
+        " 'size',\n",
+        " 'swap',\n",
+        " 'this',\n",
+        " 'thisown',\n",
+        " 'upper_bound']"
+       ]
+      }
+     ],
+     "prompt_number": 17
+    },
     {
      "cell_type": "code",
      "collapsed": false,
@@ -1333,7 +1413,7 @@
      "language": "python",
      "metadata": {},
      "outputs": [],
-     "prompt_number": 14
+     "prompt_number": 15
     },
     {
      "cell_type": "code",
@@ -1347,13 +1427,13 @@
       {
        "metadata": {},
        "output_type": "pyout",
-       "prompt_number": 15,
+       "prompt_number": 16,
        "text": [
         "False"
        ]
       }
      ],
-     "prompt_number": 15
+     "prompt_number": 16
     }
    ],
    "metadata": {}