diff --git a/Project.toml b/Project.toml
index 0f33f77..5bdc0d6 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "HierarchicalUtils"
 uuid = "f9ccea15-0695-44b9-8113-df7c26ae4fa9"
 authors = ["Simon Mandlik <simon.mandlik@gmail.com>"]
-version = "1.1.0"
+version = "1.2.0"
 
 [deps]
 DataStructures = "864edb3b-99cc-5e75-8d2d-829cb0a9cfe8"
diff --git a/examples/expression_tree.ipynb b/examples/expression_tree.ipynb
index 3b863c2..0a6f7d8 100644
--- a/examples/expression_tree.ipynb
+++ b/examples/expression_tree.ipynb
@@ -9,7 +9,9 @@
      "name": "stderr",
      "output_type": "stream",
      "text": [
-      "\u001b[32m\u001b[1m Activating\u001b[22m\u001b[39m environment at `~/.julia/dev/HierarchicalUtils/examples/Project.toml`\n"
+      "\u001b[32m\u001b[1m Activating\u001b[22m\u001b[39m environment at `~/.julia/dev/HierarchicalUtils/examples/Project.toml`\n",
+      "┌ Info: Precompiling HierarchicalUtils [f9ccea15-0695-44b9-8113-df7c26ae4fa9]\n",
+      "└ @ Base loading.jl:1278\n"
      ]
     }
    ],
@@ -82,7 +84,9 @@
     "To obtain `HierarchicalUtils` functionality, one must provide the following method/trait definitions:\n",
     "\n",
     "- `NodeType(::Type{MyType})` equal to `HierarchicalUtils.LeafNode()` in case when nodes of the given type are always leaves in the tree (in our case `Value` and `Variable`), or equal to `HierarchicalUtils.InnerNode()` in case when node of this type can have multiple (possibly zero) children.\n",
-    "- `children(n::MyType)` returning either a `Tuple` or `NamedTuple` of children (if children are referred to by some names/keys). For `LeafNode`s, this definition is not required.\n",
+    "- `children(n::MyType)` returning \"collection\" of children. If each child is identified by some key, it is possible to return either a `NamedTuple`, a `Dict` or a `Vector` of `Pair`s. For unordered children (or number indexing), return a `Tuple`, a `Vector\n",
+    "\n",
+    "For `LeafNode`s, this definition is not required.\n",
     "\n",
     "Optionally, one can provide:\n",
     "\n",
@@ -235,15 +239,15 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "\u001b[31m/\u001b[39m\n",
-      "\u001b[31m├── op1: \u001b[39m\u001b[32m*\u001b[39m\n",
-      "\u001b[31m│        \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[33m+\u001b[39m\n",
-      "\u001b[31m│        \u001b[39m\u001b[32m│        \u001b[39m\u001b[33m├── op1: \u001b[39m\u001b[37m2\u001b[39m\n",
-      "\u001b[31m│        \u001b[39m\u001b[32m│        \u001b[39m\u001b[33m└── op2: \u001b[39m\u001b[37my\u001b[39m\n",
-      "\u001b[31m│        \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[37m5\u001b[39m\n",
-      "\u001b[31m└── op2: \u001b[39m\u001b[32m-\u001b[39m\n",
-      "\u001b[31m         \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[37m4\u001b[39m\n",
-      "\u001b[31m         \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[37mx\u001b[39m"
+      "\u001b[34m/\u001b[39m\n",
+      "\u001b[34m├── op1: \u001b[39m\u001b[31m*\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m├── op1: \u001b[39m\u001b[32m+\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m│        \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[37m2\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m│        \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[37my\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m└── op2: \u001b[39m\u001b[37m5\u001b[39m\n",
+      "\u001b[34m└── op2: \u001b[39m\u001b[31m-\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m├── op1: \u001b[39m\u001b[37m4\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m└── op2: \u001b[39m\u001b[37mx\u001b[39m"
      ]
     }
    ],
@@ -260,15 +264,15 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "\u001b[31m-\u001b[39m\n",
-      "\u001b[31m├── op1: \u001b[39m\u001b[32m+\u001b[39m\n",
-      "\u001b[31m│        \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[33m/\u001b[39m\n",
-      "\u001b[31m│        \u001b[39m\u001b[32m│        \u001b[39m\u001b[33m├── op1: \u001b[39m\u001b[37m10\u001b[39m\n",
-      "\u001b[31m│        \u001b[39m\u001b[32m│        \u001b[39m\u001b[33m└── op2: \u001b[39m\u001b[37my\u001b[39m\n",
-      "\u001b[31m│        \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[37m5\u001b[39m\n",
-      "\u001b[31m└── op2: \u001b[39m\u001b[32m*\u001b[39m\n",
-      "\u001b[31m         \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[37m8\u001b[39m\n",
-      "\u001b[31m         \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[37mz\u001b[39m"
+      "\u001b[34m-\u001b[39m\n",
+      "\u001b[34m├── op1: \u001b[39m\u001b[31m+\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m├── op1: \u001b[39m\u001b[32m/\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m│        \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[37m10\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m│        \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[37my\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m└── op2: \u001b[39m\u001b[37m5\u001b[39m\n",
+      "\u001b[34m└── op2: \u001b[39m\u001b[31m*\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m├── op1: \u001b[39m\u001b[37m8\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m└── op2: \u001b[39m\u001b[37mz\u001b[39m"
      ]
     }
    ],
@@ -303,15 +307,15 @@
     {
      "data": {
       "text/plain": [
-       "\u001b[31m/\u001b[39m\n",
-       "\u001b[31m├── op1: \u001b[39m\u001b[32m*\u001b[39m\n",
-       "\u001b[31m│        \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[33m+\u001b[39m\n",
-       "\u001b[31m│        \u001b[39m\u001b[32m│        \u001b[39m\u001b[33m├── op1: \u001b[39m\u001b[37m2\u001b[39m\n",
-       "\u001b[31m│        \u001b[39m\u001b[32m│        \u001b[39m\u001b[33m└── op2: \u001b[39m\u001b[37my\u001b[39m\n",
-       "\u001b[31m│        \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[37m5\u001b[39m\n",
-       "\u001b[31m└── op2: \u001b[39m\u001b[32m-\u001b[39m\n",
-       "\u001b[31m         \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[37m4\u001b[39m\n",
-       "\u001b[31m         \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[37mx\u001b[39m"
+       "\u001b[34m/\u001b[39m\n",
+       "\u001b[34m├── op1: \u001b[39m\u001b[31m*\u001b[39m\n",
+       "\u001b[34m│        \u001b[39m\u001b[31m├── op1: \u001b[39m\u001b[32m+\u001b[39m\n",
+       "\u001b[34m│        \u001b[39m\u001b[31m│        \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[37m2\u001b[39m\n",
+       "\u001b[34m│        \u001b[39m\u001b[31m│        \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[37my\u001b[39m\n",
+       "\u001b[34m│        \u001b[39m\u001b[31m└── op2: \u001b[39m\u001b[37m5\u001b[39m\n",
+       "\u001b[34m└── op2: \u001b[39m\u001b[31m-\u001b[39m\n",
+       "\u001b[34m         \u001b[39m\u001b[31m├── op1: \u001b[39m\u001b[37m4\u001b[39m\n",
+       "\u001b[34m         \u001b[39m\u001b[31m└── op2: \u001b[39m\u001b[37mx\u001b[39m"
       ]
      },
      "execution_count": 11,
@@ -327,28 +331,78 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Truncating large trees"
+    "Truncating large trees both horizontally and vertically"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 12,
+   "execution_count": 27,
    "metadata": {},
    "outputs": [
     {
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "\u001b[31m/\u001b[39m\n",
-      "\u001b[31m├── op1: \u001b[39m\u001b[32m*\u001b[39m\n",
-      "\u001b[31m│        \u001b[39m\u001b[32m⋮\u001b[39m\n",
-      "\u001b[31m└── op2: \u001b[39m\u001b[32m-\u001b[39m\n",
-      "\u001b[31m         \u001b[39m\u001b[32m⋮\u001b[39m"
+      "(vtrunc, htrunc) = (1, 1)\n",
+      "\u001b[34m/\u001b[39m\n",
+      "\u001b[34m⋮\u001b[39m\n",
+      "(vtrunc, htrunc) = (1, 2)\n",
+      "\u001b[34m/\u001b[39m\n",
+      "\u001b[34m├── op1: \u001b[39m\u001b[31m*\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m⋮\u001b[39m\n",
+      "\u001b[34m│      ⋮\u001b[39m\n",
+      "(vtrunc, htrunc) = (1, 3)\n",
+      "\u001b[34m/\u001b[39m\n",
+      "\u001b[34m├── op1: \u001b[39m\u001b[31m*\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m├── op1: \u001b[39m\u001b[32m+\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m│        \u001b[39m\u001b[32m⋮\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m│      ⋮\u001b[39m\n",
+      "\u001b[34m│      ⋮\u001b[39m\n",
+      "(vtrunc, htrunc) = (2, 1)\n",
+      "\u001b[34m/\u001b[39m\n",
+      "\u001b[34m⋮\u001b[39m\n",
+      "(vtrunc, htrunc) = (2, 2)\n",
+      "\u001b[34m/\u001b[39m\n",
+      "\u001b[34m├── op1: \u001b[39m\u001b[31m*\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m⋮\u001b[39m\n",
+      "\u001b[34m└── op2: \u001b[39m\u001b[31m-\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m⋮\u001b[39m\n",
+      "(vtrunc, htrunc) = (2, 3)\n",
+      "\u001b[34m/\u001b[39m\n",
+      "\u001b[34m├── op1: \u001b[39m\u001b[31m*\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m├── op1: \u001b[39m\u001b[32m+\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m│        \u001b[39m\u001b[32m⋮\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m└── op2: \u001b[39m\u001b[37m5\u001b[39m\n",
+      "\u001b[34m└── op2: \u001b[39m\u001b[31m-\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m├── op1: \u001b[39m\u001b[37m4\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m└── op2: \u001b[39m\u001b[37mx\u001b[39m\n",
+      "(vtrunc, htrunc) = (3, 1)\n",
+      "\u001b[34m/\u001b[39m\n",
+      "\u001b[34m⋮\u001b[39m\n",
+      "(vtrunc, htrunc) = (3, 2)\n",
+      "\u001b[34m/\u001b[39m\n",
+      "\u001b[34m├── op1: \u001b[39m\u001b[31m*\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m⋮\u001b[39m\n",
+      "\u001b[34m└── op2: \u001b[39m\u001b[31m-\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m⋮\u001b[39m\n",
+      "(vtrunc, htrunc) = (3, 3)\n",
+      "\u001b[34m/\u001b[39m\n",
+      "\u001b[34m├── op1: \u001b[39m\u001b[31m*\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m├── op1: \u001b[39m\u001b[32m+\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m│        \u001b[39m\u001b[32m⋮\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m└── op2: \u001b[39m\u001b[37m5\u001b[39m\n",
+      "\u001b[34m└── op2: \u001b[39m\u001b[31m-\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m├── op1: \u001b[39m\u001b[37m4\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m└── op2: \u001b[39m\u001b[37mx\u001b[39m\n"
      ]
     }
    ],
    "source": [
-    "printtree(t1; trunc=2)"
+    "for vtrunc in 1:3, htrunc in 1:3\n",
+    "    @show vtrunc, htrunc\n",
+    "    printtree(t1; vtrunc, htrunc)\n",
+    "    println()\n",
+    "end"
    ]
   },
   {
@@ -367,22 +421,22 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 13,
+   "execution_count": 28,
    "metadata": {},
    "outputs": [
     {
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "\u001b[31m/ [\"\"]\u001b[39m\n",
-      "\u001b[31m├── op1: \u001b[39m\u001b[32m* [\"E\"]\u001b[39m\n",
-      "\u001b[31m│        \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[33m+ [\"I\"]\u001b[39m\n",
-      "\u001b[31m│        \u001b[39m\u001b[32m│        \u001b[39m\u001b[33m├── op1: \u001b[39m\u001b[37m2 [\"J\"]\u001b[39m\n",
-      "\u001b[31m│        \u001b[39m\u001b[32m│        \u001b[39m\u001b[33m└── op2: \u001b[39m\u001b[37my [\"K\"]\u001b[39m\n",
-      "\u001b[31m│        \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[37m5 [\"M\"]\u001b[39m\n",
-      "\u001b[31m└── op2: \u001b[39m\u001b[32m- [\"U\"]\u001b[39m\n",
-      "\u001b[31m         \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[37m4 [\"Y\"]\u001b[39m\n",
-      "\u001b[31m         \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[37mx [\"c\"]\u001b[39m"
+      "\u001b[34m/ [\"\"]\u001b[39m\n",
+      "\u001b[34m├── op1: \u001b[39m\u001b[31m* [\"E\"]\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m├── op1: \u001b[39m\u001b[32m+ [\"I\"]\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m│        \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[37m2 [\"J\"]\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m│        \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[37my [\"K\"]\u001b[39m\n",
+      "\u001b[34m│        \u001b[39m\u001b[31m└── op2: \u001b[39m\u001b[37m5 [\"M\"]\u001b[39m\n",
+      "\u001b[34m└── op2: \u001b[39m\u001b[31m- [\"U\"]\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m├── op1: \u001b[39m\u001b[37m4 [\"Y\"]\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m└── op2: \u001b[39m\u001b[37mx [\"c\"]\u001b[39m"
      ]
     }
    ],
@@ -399,7 +453,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 14,
+   "execution_count": 29,
    "metadata": {},
    "outputs": [
     {
@@ -408,7 +462,7 @@
        "\"I\""
       ]
      },
-     "execution_count": 14,
+     "execution_count": 29,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -426,18 +480,18 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 15,
+   "execution_count": 30,
    "metadata": {},
    "outputs": [
     {
      "data": {
       "text/plain": [
-       "\u001b[31m+\u001b[39m\n",
-       "\u001b[31m├── op1: \u001b[39m\u001b[37m2\u001b[39m\n",
-       "\u001b[31m└── op2: \u001b[39m\u001b[37my\u001b[39m"
+       "\u001b[34m+\u001b[39m\n",
+       "\u001b[34m├── op1: \u001b[39m\u001b[37m2\u001b[39m\n",
+       "\u001b[34m└── op2: \u001b[39m\u001b[37my\u001b[39m"
       ]
      },
-     "execution_count": 15,
+     "execution_count": 30,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -455,7 +509,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 16,
+   "execution_count": 31,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -482,7 +536,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 17,
+   "execution_count": 32,
    "metadata": {},
    "outputs": [
     {
@@ -491,7 +545,7 @@
        "true"
       ]
      },
-     "execution_count": 17,
+     "execution_count": 32,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -509,23 +563,23 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 18,
+   "execution_count": 33,
    "metadata": {},
    "outputs": [
     {
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "\u001b[31m+\u001b[39m\n",
-      "\u001b[31m├── op1: \u001b[39m\u001b[37m1\u001b[39m\n",
-      "\u001b[31m└── op2: \u001b[39m\u001b[32m/\u001b[39m\n",
-      "\u001b[31m         \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[37m1\u001b[39m\n",
-      "\u001b[31m         \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[33m+\u001b[39m\n",
-      "\u001b[31m         \u001b[39m\u001b[32m         \u001b[39m\u001b[33m├── op1: \u001b[39m\u001b[37m1\u001b[39m\n",
-      "\u001b[31m         \u001b[39m\u001b[32m         \u001b[39m\u001b[33m└── op2: \u001b[39m\u001b[36m/\u001b[39m\n",
-      "\u001b[31m         \u001b[39m\u001b[32m         \u001b[39m\u001b[33m         \u001b[39m\u001b[36m├── op1: \u001b[39m\u001b[37m1\u001b[39m\n",
-      "\u001b[31m         \u001b[39m\u001b[32m         \u001b[39m\u001b[33m         \u001b[39m\u001b[36m└── op2: \u001b[39m\u001b[35m+\u001b[39m\n",
-      "\u001b[31m         \u001b[39m\u001b[32m         \u001b[39m\u001b[33m         \u001b[39m\u001b[36m         \u001b[39m\u001b[35m⋮\u001b[39m"
+      "\u001b[34m+\u001b[39m\n",
+      "\u001b[34m├── op1: \u001b[39m\u001b[37m1\u001b[39m\n",
+      "\u001b[34m└── op2: \u001b[39m\u001b[31m/\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m├── op1: \u001b[39m\u001b[37m1\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m└── op2: \u001b[39m\u001b[32m+\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m         \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[37m1\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m         \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[33m/\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m         \u001b[39m\u001b[32m         \u001b[39m\u001b[33m├── op1: \u001b[39m\u001b[37m1\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m         \u001b[39m\u001b[32m         \u001b[39m\u001b[33m└── op2: \u001b[39m\u001b[36m+\u001b[39m\n",
+      "\u001b[34m         \u001b[39m\u001b[31m         \u001b[39m\u001b[32m         \u001b[39m\u001b[33m         \u001b[39m\u001b[36m⋮\u001b[39m"
      ]
     }
    ],
@@ -535,7 +589,7 @@
     "t_golden[2,2] = t_golden;\n",
     "t_golden[2][2] = t_golden;\n",
     "t_golden.ch[2][2] = t_golden;\n",
-    "printtree(t_golden; trunc=5)"
+    "printtree(t_golden; htrunc=5)"
    ]
   },
   {
@@ -547,7 +601,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 19,
+   "execution_count": 34,
    "metadata": {},
    "outputs": [
     {
@@ -565,7 +619,7 @@
        " \"c\""
       ]
      },
-     "execution_count": 19,
+     "execution_count": 34,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -589,8 +643,8 @@
     "\n",
     "- `NodeIterator(t; complete::Bool=true, order::AbstractOrder=PreOrder())` iterates over all nodes in the tree\n",
     "- `LeafIterator(t; complete::Bool=true, order::AbstractOrder=PreOrder())` iterates over all leaves (either nodes marked with `LeafNode()` trait or `InnerNode()` with zero children)\n",
-    "- `TypeIterator(t, type::Type; complete::Bool=true, order::AbstractOrder=PreOrder())` iterates over all nodes of the given type\n",
-    "- `PredicateIterator(t, f::Function; complete::Bool=true, order::AbstractOrder=PreOrder())` iterates over all nodes, such that `f(n)` returns true"
+    "- `TypeIterator(type::Type, t; complete::Bool=true, order::AbstractOrder=PreOrder())` iterates over all nodes of the given type\n",
+    "- `PredicateIterator(f::Function, t; complete::Bool=true, order::AbstractOrder=PreOrder())` iterates over all nodes, such that `f(n)` returns true"
    ]
   },
   {
@@ -602,24 +656,24 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 20,
+   "execution_count": 35,
    "metadata": {},
    "outputs": [
     {
      "data": {
       "text/plain": [
-       "\u001b[31m/\u001b[39m\n",
-       "\u001b[31m├── op1: \u001b[39m\u001b[32m*\u001b[39m\n",
-       "\u001b[31m│        \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[33m+\u001b[39m\n",
-       "\u001b[31m│        \u001b[39m\u001b[32m│        \u001b[39m\u001b[33m├── op1: \u001b[39m\u001b[37m2\u001b[39m\n",
-       "\u001b[31m│        \u001b[39m\u001b[32m│        \u001b[39m\u001b[33m└── op2: \u001b[39m\u001b[37my\u001b[39m\n",
-       "\u001b[31m│        \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[37m5\u001b[39m\n",
-       "\u001b[31m└── op2: \u001b[39m\u001b[32m-\u001b[39m\n",
-       "\u001b[31m         \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[37m4\u001b[39m\n",
-       "\u001b[31m         \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[37mx\u001b[39m"
+       "\u001b[34m/\u001b[39m\n",
+       "\u001b[34m├── op1: \u001b[39m\u001b[31m*\u001b[39m\n",
+       "\u001b[34m│        \u001b[39m\u001b[31m├── op1: \u001b[39m\u001b[32m+\u001b[39m\n",
+       "\u001b[34m│        \u001b[39m\u001b[31m│        \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[37m2\u001b[39m\n",
+       "\u001b[34m│        \u001b[39m\u001b[31m│        \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[37my\u001b[39m\n",
+       "\u001b[34m│        \u001b[39m\u001b[31m└── op2: \u001b[39m\u001b[37m5\u001b[39m\n",
+       "\u001b[34m└── op2: \u001b[39m\u001b[31m-\u001b[39m\n",
+       "\u001b[34m         \u001b[39m\u001b[31m├── op1: \u001b[39m\u001b[37m4\u001b[39m\n",
+       "\u001b[34m         \u001b[39m\u001b[31m└── op2: \u001b[39m\u001b[37mx\u001b[39m"
       ]
      },
-     "execution_count": 20,
+     "execution_count": 35,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -630,24 +684,24 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 21,
+   "execution_count": 36,
    "metadata": {},
    "outputs": [
     {
      "data": {
       "text/plain": [
-       "\u001b[31m-\u001b[39m\n",
-       "\u001b[31m├── op1: \u001b[39m\u001b[32m+\u001b[39m\n",
-       "\u001b[31m│        \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[33m/\u001b[39m\n",
-       "\u001b[31m│        \u001b[39m\u001b[32m│        \u001b[39m\u001b[33m├── op1: \u001b[39m\u001b[37m10\u001b[39m\n",
-       "\u001b[31m│        \u001b[39m\u001b[32m│        \u001b[39m\u001b[33m└── op2: \u001b[39m\u001b[37my\u001b[39m\n",
-       "\u001b[31m│        \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[37m5\u001b[39m\n",
-       "\u001b[31m└── op2: \u001b[39m\u001b[32m*\u001b[39m\n",
-       "\u001b[31m         \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[37m8\u001b[39m\n",
-       "\u001b[31m         \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[37mz\u001b[39m"
+       "\u001b[34m-\u001b[39m\n",
+       "\u001b[34m├── op1: \u001b[39m\u001b[31m+\u001b[39m\n",
+       "\u001b[34m│        \u001b[39m\u001b[31m├── op1: \u001b[39m\u001b[32m/\u001b[39m\n",
+       "\u001b[34m│        \u001b[39m\u001b[31m│        \u001b[39m\u001b[32m├── op1: \u001b[39m\u001b[37m10\u001b[39m\n",
+       "\u001b[34m│        \u001b[39m\u001b[31m│        \u001b[39m\u001b[32m└── op2: \u001b[39m\u001b[37my\u001b[39m\n",
+       "\u001b[34m│        \u001b[39m\u001b[31m└── op2: \u001b[39m\u001b[37m5\u001b[39m\n",
+       "\u001b[34m└── op2: \u001b[39m\u001b[31m*\u001b[39m\n",
+       "\u001b[34m         \u001b[39m\u001b[31m├── op1: \u001b[39m\u001b[37m8\u001b[39m\n",
+       "\u001b[34m         \u001b[39m\u001b[31m└── op2: \u001b[39m\u001b[37mz\u001b[39m"
       ]
      },
-     "execution_count": 21,
+     "execution_count": 36,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -658,18 +712,18 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 22,
+   "execution_count": 37,
    "metadata": {},
    "outputs": [
     {
      "data": {
       "text/plain": [
-       "\u001b[31m+\u001b[39m\n",
-       "\u001b[31m├── op1: \u001b[39m\u001b[37mx\u001b[39m\n",
-       "\u001b[31m└── op2: \u001b[39m\u001b[37my\u001b[39m"
+       "\u001b[34m+\u001b[39m\n",
+       "\u001b[34m├── op1: \u001b[39m\u001b[37mx\u001b[39m\n",
+       "\u001b[34m└── op2: \u001b[39m\u001b[37my\u001b[39m"
       ]
      },
-     "execution_count": 22,
+     "execution_count": 37,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -680,7 +734,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 23,
+   "execution_count": 38,
    "metadata": {},
    "outputs": [
     {
@@ -690,15 +744,15 @@
        " /\n",
        " *\n",
        " +\n",
-       " 2\n",
-       " y\n",
-       " 5\n",
+       " \u001b[37m2\u001b[39m\n",
+       " \u001b[37my\u001b[39m\n",
+       " \u001b[37m5\u001b[39m\n",
        " -\n",
-       " 4\n",
-       " x"
+       " \u001b[37m4\u001b[39m\n",
+       " \u001b[37mx\u001b[39m"
       ]
      },
-     "execution_count": 23,
+     "execution_count": 38,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -709,21 +763,21 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 24,
+   "execution_count": 39,
    "metadata": {},
    "outputs": [
     {
      "data": {
       "text/plain": [
        "5-element Array{Expression,1}:\n",
-       " 2\n",
-       " y\n",
-       " 5\n",
-       " 4\n",
-       " x"
+       " \u001b[37m2\u001b[39m\n",
+       " \u001b[37my\u001b[39m\n",
+       " \u001b[37m5\u001b[39m\n",
+       " \u001b[37m4\u001b[39m\n",
+       " \u001b[37mx\u001b[39m"
       ]
      },
-     "execution_count": 24,
+     "execution_count": 39,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -1381,15 +1435,15 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "Julia 1.4.1",
+   "display_name": "Julia 1.5.0",
    "language": "julia",
-   "name": "julia-1.4"
+   "name": "julia-1.5"
   },
   "language_info": {
    "file_extension": ".jl",
    "mimetype": "application/julia",
    "name": "julia",
-   "version": "1.4.1"
+   "version": "1.5.0"
   }
  },
  "nbformat": 4,
diff --git a/src/definitions.jl b/src/definitions.jl
index 86c36fb..fba6041 100644
--- a/src/definitions.jl
+++ b/src/definitions.jl
@@ -1,4 +1,3 @@
-# TODO define this implicitly?
 macro hierarchical_dict()
     return esc(
                quote