Using / instead of - as suggested by @boldip

Author: mapio

notebook.ipynb

@@ -262,7 +262,7 @@
    "source": [
     "## Basic algebraic facts about transformations\n",
     "\n",
-    "Such transformations can be also implemented as binary operators (thanks to Python ability to define classes that [emulate numeric types](https://docs.python.org/3/reference/datamodel.html#emulating-numeric-types)); one can for instance use `|` and `-` respectively for `beside` and `above` (the minus is to be understood as an horizontal line), and `+` for `over`."
+    "Such transformations can be also implemented as binary operators (thanks to Python ability to define classes that [emulate numeric types](https://docs.python.org/3/reference/datamodel.html#emulating-numeric-types)); one can for instance use `|` and `/` respectively for `beside` and `above`, and `+` for `over`."
    ]
   },
   {
@@ -283,7 +283,7 @@
     "        return t\n",
     "    def __add__(self, other):\n",
     "        return TileWithOperations.addop(over(self, other))\n",
-    "    def __sub__(self, other):\n",
+    "    def __truediv__(self, other):\n",
     "        return TileWithOperations.addop(above(self, other))\n",
     "    def __or__(self, other):\n",
     "        return TileWithOperations.addop(beside(self, other))\n",
@@ -297,7 +297,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "f - ( f | f )"
+    "f / ( f | f )"
    ]
   },
   {
@@ -442,7 +442,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "the flipped `F` takes $2/5$ of the final tile, whereas `F` takes the other $3/5$. Using such extended transformations one can define"
+    "the flipped `f` takes $2/5$ of the final tile, whereas `f` takes the other $3/5$. Using such extended transformations one can define"
    ]
   },
   {