diff --git a/resources/NBTest/NBTest_051_CPCBalancer.ipynb b/resources/NBTest/NBTest_051_CPCBalancer.ipynb
index 4a8ff6bc8..06b8851f4 100644
--- a/resources/NBTest/NBTest_051_CPCBalancer.ipynb
+++ b/resources/NBTest/NBTest_051_CPCBalancer.ipynb
@@ -2,7 +2,7 @@
  "cells": [
   {
    "cell_type": "code",
-   "execution_count": 79,
+   "execution_count": 81,
    "id": "a448e212",
    "metadata": {},
    "outputs": [
@@ -10,16 +10,16 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "ConstantProductCurve v3.1beta1 (25/Aug/2023)\n"
+      "ConstantProductCurve v3.1 (25/Aug/2023)\n"
      ]
     }
    ],
    "source": [
-    "from fastlane_bot.tools.cpc import ConstantProductCurve as CPC\n",
+    "from fastlane_bot.tools.cpc import ConstantProductCurve as CPC, CurveBase\n",
     "from fastlane_bot.testing import *\n",
+    "# from flbtools.cpc import ConstantProductCurve as CPC, CurveBase\n",
+    "# from flbtesting import *\n",
     "\n",
-    "#from flbtools.cpc import ConstantProductCurve as CPC\n",
-    "#from flbtesting import *\n",
     "from math import sqrt\n",
     "print(\"{0.__name__} v{0.__VERSION__} ({0.__DATE__})\".format(CPC))\n",
     "# from fastlane_bot import __VERSION__\n",
@@ -44,19 +44,23 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 80,
+   "execution_count": 82,
    "id": "5e055a74-6e99-4ffa-a450-5f53ae7695e5",
    "metadata": {},
    "outputs": [],
    "source": [
     "c0 = CPC.from_xy(100, 200)\n",
     "assert c0.tknx == \"TKNB\"\n",
-    "assert c0.tkny == \"TKNQ\""
+    "assert c0.tkny == \"TKNQ\"\n",
+    "k0 = c0.invariant()\n",
+    "assert iseq(k0, sqrt(100*200))\n",
+    "k1, k2 = c0.invariant(include_target=True)\n",
+    "assert iseq(k0, k1, k2)"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 81,
+   "execution_count": 83,
    "id": "22004cc1-b2c4-4486-b16f-f8a7b4fbd1b8",
    "metadata": {},
    "outputs": [],
@@ -67,13 +71,14 @@
     "assert iseq(y, 200)\n",
     "assert iseq(xvec[c0.tknx], x)\n",
     "assert iseq(xvec[c0.tkny], y)\n",
+    "assert iseq(c0.invariant(), c0.invariant(xvec))\n",
     "assert raises(c0.xvecfrompvec_f, {c0.tknx: c0.p} ).startswith(\"pvec must contain\")\n",
     "assert raises(c0.xvecfrompvec_f, {c0.tkny: 1} ).startswith(\"pvec must contain\")"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 82,
+   "execution_count": 84,
    "id": "4138bcb3-0054-4077-8a0d-df39cb46f98f",
    "metadata": {},
    "outputs": [],
@@ -88,12 +93,13 @@
     "assert iseq(x, 81.64965809277261)\n",
     "assert iseq(y, 244.9489742783178)\n",
     "assert iseq(xvec[c0.tknx], x)\n",
-    "assert iseq(xvec[c0.tkny], y)"
+    "assert iseq(xvec[c0.tkny], y)\n",
+    "assert iseq(c0.invariant(), c0.invariant(xvec))"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 83,
+   "execution_count": 85,
    "id": "ffa625ad-6ca5-40fe-b20a-bede3249cc7e",
    "metadata": {},
    "outputs": [],
@@ -110,7 +116,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 84,
+   "execution_count": 86,
    "id": "4975e630-45ba-4ac2-95ed-2809b6488f4a",
    "metadata": {},
    "outputs": [],
@@ -128,6 +134,64 @@
     "assert iseq(dxvec[c0.tkny], dy)"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "id": "bc39d223-0e37-43f4-86f0-1c07105cb321",
+   "metadata": {},
+   "source": [
+    "## CurveBase"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "1bb551a7-0e40-4758-ae87-1d1b30f12a3f",
+   "metadata": {},
+   "source": [
+    "Checking that `CurveBase` can only instantiate with all functions defined"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 87,
+   "id": "5ba59a93-f792-428a-8381-56f3b4b3fd30",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "class CB1(CurveBase):\n",
+    "    pass\n",
+    "\n",
+    "class CB2(CurveBase):\n",
+    "    def dxvecfrompvec_f(self, pvec, *, ignorebounds=False):\n",
+    "        pass\n",
+    "\n",
+    "class CB3(CurveBase):\n",
+    "    def xvecfrompvec_f(self, pvec, *, ignorebounds=False):\n",
+    "        pass\n",
+    "\n",
+    "class CB4(CurveBase):\n",
+    "    def xvecfrompvec_f(self, pvec, *, ignorebounds=False):\n",
+    "        pass\n",
+    "    def dxvecfrompvec_f(self, pvec, *, ignorebounds=False):\n",
+    "        pass\n",
+    "    def invariant(self, xvec=None, *, include_target=False):\n",
+    "        pass\n",
+    "    \n",
+    "assert raises(CB1).startswith(\"Can't instantiate abstract class\")\n",
+    "assert raises(CB2).startswith(\"Can't instantiate abstract class\")\n",
+    "assert raises(CB3).startswith(\"Can't instantiate abstract class\")\n",
+    "assert not raises(CB4)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 88,
+   "id": "afb61a79-c802-41f0-bafa-4d2ae4bc82d5",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "assert isinstance(CPC.from_xy(100, 200), CurveBase)"
+   ]
+  },
   {
    "cell_type": "markdown",
    "id": "521e4bc5-f003-4062-8978-18506ecff248",
@@ -138,7 +202,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 85,
+   "execution_count": 89,
    "id": "c5cf94f7-77df-412c-9988-7085184bdd1f",
    "metadata": {},
    "outputs": [
@@ -148,7 +212,7 @@
        "ConstantProductCurve(k=20000, x=100, x_act=100, y_act=200.0, alpha=0.5, pair='TKNB/TKNQ', cid='None', fee=None, descr=None, constr='xy', params={})"
       ]
      },
-     "execution_count": 85,
+     "execution_count": 89,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -169,7 +233,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 86,
+   "execution_count": 90,
    "id": "9eb7484e-a09a-4184-bd59-073a7b399b8a",
    "metadata": {},
    "outputs": [],
@@ -191,7 +255,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 87,
+   "execution_count": 91,
    "id": "2b12d88d-6d7d-4d39-b9bc-def990500df7",
    "metadata": {},
    "outputs": [
@@ -201,7 +265,7 @@
        "ConstantProductCurve(k=20000.0, x=100, x_act=100, y_act=200.0, alpha=0.5, pair='TKNB/TKNQ', cid='None', fee=None, descr=None, constr='xyal', params={})"
       ]
      },
-     "execution_count": 87,
+     "execution_count": 91,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -216,7 +280,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 88,
+   "execution_count": 92,
    "id": "fc98b1e0-0771-4cd6-877c-b70e74b548b8",
    "metadata": {},
    "outputs": [],
@@ -238,7 +302,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 89,
+   "execution_count": 93,
    "id": "f6ededab-423a-489e-8d1b-295162fda59b",
    "metadata": {},
    "outputs": [
@@ -248,7 +312,7 @@
        "ConstantProductCurve(k=20000.0, x=100, x_act=100, y_act=200.0, alpha=0.5, pair='TKNB/TKNQ', cid='None', fee=None, descr=None, constr='xyal', params={})"
       ]
      },
-     "execution_count": 89,
+     "execution_count": 93,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -264,7 +328,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 90,
+   "execution_count": 94,
    "id": "203e5e7b-1cde-4154-a75c-35068f018a21",
    "metadata": {},
    "outputs": [
@@ -274,7 +338,7 @@
        "ConstantProductCurve(k=20000.0, x=100, x_act=100, y_act=200.0, alpha=0.5, pair='TKNB/TKNQ', cid='None', fee=None, descr=None, constr='xyal', params={})"
       ]
      },
-     "execution_count": 90,
+     "execution_count": 94,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -290,7 +354,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 91,
+   "execution_count": 95,
    "id": "ee693b31-3278-46d2-a578-ba6e0b2c6333",
    "metadata": {},
    "outputs": [],
@@ -309,7 +373,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 92,
+   "execution_count": 96,
    "id": "2331941a-3aeb-4fa3-887a-6ed45c37307b",
    "metadata": {},
    "outputs": [
@@ -319,7 +383,7 @@
        "ConstantProductCurve(k=20000, x=100, x_act=100, y_act=200.0, alpha=0.5, pair='TKNB/TKNQ', cid='None', fee=None, descr=None, constr='xy', params={})"
       ]
      },
-     "execution_count": 92,
+     "execution_count": 96,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -334,13 +398,22 @@
     "assert c0.alpha == 0.5\n",
     "assert c0.eta == 1\n",
     "assert c0.constr == \"xy\"\n",
+    "assert iseq(c0.invariant(), c0.kbar)\n",
     "assert c0.is_constant_product() == True\n",
     "c0"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 93,
+   "execution_count": null,
+   "id": "00857b2e-d9af-41ce-a41f-c52b373fcd3a",
+   "metadata": {},
+   "outputs": [],
+   "source": []
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 97,
    "id": "db5f6d9a-87c3-4bba-9bbc-32993d2c09a7",
    "metadata": {},
    "outputs": [
@@ -350,7 +423,7 @@
        "ConstantProductCurve(k=20000.0, x=100, x_act=100, y_act=200.0, alpha=0.5, pair='TKNB/TKNQ', cid='None', fee=None, descr=None, constr='xyal', params={})"
       ]
      },
-     "execution_count": 93,
+     "execution_count": 97,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -361,12 +434,13 @@
     "assert c1.is_constant_product() == True\n",
     "assert c1 == c0\n",
     "assert c1.asdict()[\"alpha\"] == 0.5\n",
+    "assert iseq(c1.invariant(), c1.kbar)\n",
     "c1"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 94,
+   "execution_count": 98,
    "id": "02dc9cc9-d30e-4daf-9f7d-11f9bd60ad04",
    "metadata": {},
    "outputs": [
@@ -376,7 +450,7 @@
        "ConstantProductCurve(k=800000000.0, x=100, x_act=100, y_act=199.99999999999994, alpha=0.25, pair='TKNB/TKNQ', cid='None', fee=None, descr=None, constr='xyal', params={})"
       ]
      },
-     "execution_count": 94,
+     "execution_count": 98,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -388,6 +462,7 @@
     "assert c2.alpha == 0.25\n",
     "assert c2.asdict()[\"alpha\"] == 0.25\n",
     "assert iseq(c2.eta, 0.25/0.75)\n",
+    "assert iseq(c2.invariant(), c2.kbar)\n",
     "assert c2 != c0\n",
     "assert c2 != c1\n",
     "c2"
@@ -395,7 +470,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 95,
+   "execution_count": 99,
    "id": "f48bec87-6674-4a5c-8a15-562c5caff154",
    "metadata": {},
    "outputs": [
@@ -405,7 +480,7 @@
        "ConstantProductCurve(k=800000000.0, x=100, x_act=100, y_act=199.99999999999994, alpha=0.25, pair='TKNB/TKNQ', cid='None', fee=None, descr=None, constr='xyal', params={})"
       ]
      },
-     "execution_count": 95,
+     "execution_count": 99,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -417,6 +492,7 @@
     "assert iseq(c3.alpha, 0.8)\n",
     "assert c3.asdict()[\"alpha\"] == 0.8\n",
     "assert iseq(c3.eta, 0.8/0.2)\n",
+    "assert iseq(c3.invariant(), c3.kbar)\n",
     "assert c3 != c0\n",
     "assert c3 != c1\n",
     "assert c3 != c2\n",
@@ -425,7 +501,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 96,
+   "execution_count": 100,
    "id": "4dc4a1f6-1d71-4f1d-b0a0-616f83fb58e8",
    "metadata": {},
    "outputs": [
@@ -435,7 +511,7 @@
        "ConstantProductCurve(k=376.06030930863926, x=100, x_act=100, y_act=200.0, alpha=0.8, pair='TKNB/TKNQ', cid='None', fee=None, descr=None, constr='xyal', params={})"
       ]
      },
-     "execution_count": 96,
+     "execution_count": 100,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -448,7 +524,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 97,
+   "execution_count": 101,
    "id": "8caba1ff-65e7-496e-adcf-aea4cddcee4b",
    "metadata": {},
    "outputs": [],
@@ -461,7 +537,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 98,
+   "execution_count": 102,
    "id": "b54669fb-a128-41ae-a3ac-b9eff553f897",
    "metadata": {},
    "outputs": [
@@ -471,7 +547,7 @@
        "'alpha must be > 0 [0]'"
       ]
      },
-     "execution_count": 98,
+     "execution_count": 102,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -482,7 +558,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 99,
+   "execution_count": 103,
    "id": "c4630e2a-b577-410b-8251-1c327866c9f1",
    "metadata": {},
    "outputs": [],
@@ -493,7 +569,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 100,
+   "execution_count": 104,
    "id": "c8c740c3-3ffb-4694-95dc-2932b7d39c6c",
    "metadata": {},
    "outputs": [
@@ -503,7 +579,7 @@
        "\"(34, 'Result too large')\""
       ]
      },
-     "execution_count": 100,
+     "execution_count": 104,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -524,7 +600,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 101,
+   "execution_count": 105,
    "id": "fd739374-c01b-432e-ab80-98e35fda3674",
    "metadata": {},
    "outputs": [
@@ -534,7 +610,7 @@
        "ConstantProductCurve(k=20000.0, x=100, x_act=100, y_act=200.0, alpha=0.5, pair='TKNB/TKNQ', cid='None', fee=None, descr=None, constr='xyal', params={})"
       ]
      },
-     "execution_count": 101,
+     "execution_count": 105,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -547,7 +623,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 102,
+   "execution_count": 106,
    "id": "927269a5-0c16-4336-8fcf-3e22392c8847",
    "metadata": {},
    "outputs": [
@@ -557,7 +633,7 @@
        "ConstantProductCurve(k=800000000.0, x=100, x_act=100, y_act=199.99999999999994, alpha=0.25, pair='TKNB/TKNQ', cid='None', fee=None, descr=None, constr='xyal', params={})"
       ]
      },
-     "execution_count": 102,
+     "execution_count": 106,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -595,7 +671,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 103,
+   "execution_count": 107,
    "id": "30239c29-9c2d-4a35-b24e-593e27d23013",
    "metadata": {},
    "outputs": [],
@@ -614,7 +690,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 104,
+   "execution_count": 108,
    "id": "31973a9d-f6fc-4ba6-8660-3ca6b3b31238",
    "metadata": {},
    "outputs": [],
@@ -625,7 +701,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 105,
+   "execution_count": 109,
    "id": "6da717da-0e96-4af5-a011-74c54c5a8033",
    "metadata": {},
    "outputs": [],
@@ -644,7 +720,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 106,
+   "execution_count": 110,
    "id": "22c10615-7636-4ec9-ba02-01e9c58ad20d",
    "metadata": {},
    "outputs": [],
@@ -655,7 +731,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 107,
+   "execution_count": 111,
    "id": "b63b25fa-8f4a-415d-b0c5-8d10be06f91b",
    "metadata": {},
    "outputs": [],
@@ -666,7 +742,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 108,
+   "execution_count": 112,
    "id": "1e2a97a5-240b-49b4-abdc-f30b3b1e2788",
    "metadata": {},
    "outputs": [],
@@ -677,7 +753,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 109,
+   "execution_count": 113,
    "id": "98262a43-8c8e-4eb2-af03-6c7f082a9a5e",
    "metadata": {},
    "outputs": [],
@@ -688,7 +764,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 110,
+   "execution_count": 114,
    "id": "b3049924-bc62-44c3-b7fc-0c5513544b87",
    "metadata": {},
    "outputs": [],
@@ -699,7 +775,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 111,
+   "execution_count": 115,
    "id": "9809fe75-81eb-4117-b06f-ea80e8e5d1af",
    "metadata": {},
    "outputs": [],
@@ -718,7 +794,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 112,
+   "execution_count": 116,
    "id": "d53b7a88-b1b2-488f-b33e-cf85af69dad2",
    "metadata": {},
    "outputs": [],
@@ -729,7 +805,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 113,
+   "execution_count": 117,
    "id": "47628578-dfab-4a28-a46f-b83b12af7745",
    "metadata": {},
    "outputs": [],
@@ -740,7 +816,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 114,
+   "execution_count": 118,
    "id": "818af0e4",
    "metadata": {},
    "outputs": [],
@@ -751,7 +827,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 115,
+   "execution_count": 119,
    "id": "bac20004",
    "metadata": {},
    "outputs": [],
@@ -762,7 +838,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 116,
+   "execution_count": 120,
    "id": "490db431",
    "metadata": {},
    "outputs": [],
@@ -773,7 +849,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 117,
+   "execution_count": 121,
    "id": "bc7fda17",
    "metadata": {},
    "outputs": [],
@@ -784,7 +860,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 118,
+   "execution_count": 122,
    "id": "d1637e16-ae56-45f6-bb90-b10cd5e83194",
    "metadata": {},
    "outputs": [],
@@ -803,7 +879,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 119,
+   "execution_count": 123,
    "id": "4a70d47e-3a89-452d-80f3-d69028433648",
    "metadata": {},
    "outputs": [],
@@ -814,7 +890,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 120,
+   "execution_count": 124,
    "id": "a1bbada5-9cd2-4dd0-a226-fb7422614b53",
    "metadata": {},
    "outputs": [],
@@ -833,7 +909,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 121,
+   "execution_count": 125,
    "id": "d90a02d0-21c9-47dc-894c-82ea93b01779",
    "metadata": {},
    "outputs": [],
@@ -844,7 +920,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 122,
+   "execution_count": 126,
    "id": "052b8feb-038e-457a-a3f1-8ff25b030a0e",
    "metadata": {},
    "outputs": [],
@@ -855,7 +931,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 123,
+   "execution_count": 127,
    "id": "8872ba9c-2186-4176-add5-4a36b66162a4",
    "metadata": {},
    "outputs": [],
@@ -866,7 +942,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 124,
+   "execution_count": 128,
    "id": "795eac9c-fe49-447f-b3fe-c0268cdd20de",
    "metadata": {},
    "outputs": [],
@@ -877,7 +953,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 125,
+   "execution_count": 129,
    "id": "13b1f308-3062-4872-a91e-e89bccf17cf8",
    "metadata": {},
    "outputs": [],
@@ -889,7 +965,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 126,
+   "execution_count": 130,
    "id": "b90b56dd-bc10-4087-a3f4-5c0b8bcc681a",
    "metadata": {},
    "outputs": [],
@@ -901,7 +977,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 127,
+   "execution_count": 131,
    "id": "9b797a1f-2d04-42ae-a03f-4b9675a65ed3",
    "metadata": {},
    "outputs": [],
@@ -913,7 +989,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 128,
+   "execution_count": 132,
    "id": "ee7cd754-fe9c-4fb8-848d-46dc2850c0cd",
    "metadata": {},
    "outputs": [],
@@ -933,7 +1009,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 129,
+   "execution_count": 133,
    "id": "6373dfe5-6d20-4c55-9f0b-80a8ac6e1e05",
    "metadata": {},
    "outputs": [],
@@ -945,7 +1021,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 130,
+   "execution_count": 134,
    "id": "81cb94ae-1fd1-4d63-9f59-e79274737d4d",
    "metadata": {},
    "outputs": [],
@@ -969,7 +1045,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 131,
+   "execution_count": 135,
    "id": "0eac45f7-ef6d-419d-8254-098858e7a529",
    "metadata": {},
    "outputs": [],
@@ -993,7 +1069,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 132,
+   "execution_count": 136,
    "id": "cc39342b-1304-4e7d-8594-950df18ffb6e",
    "metadata": {},
    "outputs": [],
@@ -1017,7 +1093,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 133,
+   "execution_count": 137,
    "id": "80e3f97b-41b0-4263-b2e0-b02da963c60f",
    "metadata": {},
    "outputs": [],
@@ -1032,7 +1108,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 134,
+   "execution_count": 138,
    "id": "593fb93f-5d95-4796-9da6-abd79206ff3d",
    "metadata": {},
    "outputs": [],
@@ -1060,7 +1136,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 135,
+   "execution_count": 139,
    "id": "171b56b5-f270-4f51-8fd8-a185b3c0e91f",
    "metadata": {},
    "outputs": [],
@@ -1084,7 +1160,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 136,
+   "execution_count": 140,
    "id": "01d3e5e2-aba4-434d-a118-15bd63e854db",
    "metadata": {},
    "outputs": [],
@@ -1096,7 +1172,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 137,
+   "execution_count": 141,
    "id": "0ae9f182-0f46-4fdd-9879-619cf3f6ecd2",
    "metadata": {},
    "outputs": [],
@@ -1120,7 +1196,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 138,
+   "execution_count": 142,
    "id": "9ff8935e-1898-40b9-802f-09a7b2cc608c",
    "metadata": {},
    "outputs": [],
@@ -1133,7 +1209,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 139,
+   "execution_count": 143,
    "id": "081ec8c2-768c-45a5-a478-1df3a55590ab",
    "metadata": {},
    "outputs": [],
@@ -1146,7 +1222,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 140,
+   "execution_count": 144,
    "id": "5f556205-299f-4f5c-b717-076a64137784",
    "metadata": {},
    "outputs": [],
@@ -1173,7 +1249,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 141,
+   "execution_count": 145,
    "id": "bfbc589d-2124-4c51-9ac9-a7a3034ebd67",
    "metadata": {},
    "outputs": [],
@@ -1186,7 +1262,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 142,
+   "execution_count": 146,
    "id": "fb276d33-72b0-406d-9f3d-9ce16354098b",
    "metadata": {},
    "outputs": [],
@@ -1199,7 +1275,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 143,
+   "execution_count": 147,
    "id": "d55dd588-8a49-43c5-bf23-22fa207876fd",
    "metadata": {},
    "outputs": [],
@@ -1230,7 +1306,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 144,
+   "execution_count": 148,
    "id": "eb60778c-edd0-42c5-8681-a259e02c1e91",
    "metadata": {},
    "outputs": [],
@@ -1242,7 +1318,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 145,
+   "execution_count": 149,
    "id": "c242f036-c366-4c25-ab1d-9b13ff283d60",
    "metadata": {},
    "outputs": [],
@@ -1254,7 +1330,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 146,
+   "execution_count": 150,
    "id": "1e39b3b6-ac20-4a7d-ab4a-f764cc949ee9",
    "metadata": {},
    "outputs": [],
@@ -1283,7 +1359,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 147,
+   "execution_count": 151,
    "id": "8fd1d683-195a-414b-bfa2-2155462efcc1",
    "metadata": {},
    "outputs": [],
@@ -1296,7 +1372,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 148,
+   "execution_count": 152,
    "id": "c2a77208-d1d6-4d99-8fab-d8b9f988dac9",
    "metadata": {},
    "outputs": [],
@@ -1322,7 +1398,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 149,
+   "execution_count": 153,
    "id": "30a07eda-449f-471e-a609-f979d894d09a",
    "metadata": {},
    "outputs": [],
@@ -1348,7 +1424,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 150,
+   "execution_count": 154,
    "id": "8826b280-00f7-4771-9bc6-2d5d344b197e",
    "metadata": {},
    "outputs": [],
@@ -1369,7 +1445,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 151,
+   "execution_count": 155,
    "id": "853233ca-22bd-4d0e-a6d1-3dee13341b99",
    "metadata": {},
    "outputs": [],
@@ -1392,7 +1468,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 152,
+   "execution_count": 156,
    "id": "73dfd68b-56ba-4154-a1f8-79c8bddf4169",
    "metadata": {},
    "outputs": [],
@@ -1403,7 +1479,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 153,
+   "execution_count": 157,
    "id": "bf52087a-ffb7-4dad-bffa-753983249b51",
    "metadata": {},
    "outputs": [],
@@ -1418,7 +1494,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 154,
+   "execution_count": 158,
    "id": "c3e74ed7-83cb-497d-82a8-4a8d38bf312d",
    "metadata": {},
    "outputs": [
@@ -1446,7 +1522,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 155,
+   "execution_count": 159,
    "id": "dcf6c394-8ad0-4ea1-a0fe-849374b16110",
    "metadata": {},
    "outputs": [
@@ -1481,7 +1557,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 156,
+   "execution_count": 160,
    "id": "3c8cbd59-5039-43bc-a52d-f05201e9e83b",
    "metadata": {},
    "outputs": [
diff --git a/resources/NBTest/NBTest_051_CPCBalancer.py b/resources/NBTest/NBTest_051_CPCBalancer.py
index 04bcea464..3557fd4a4 100644
--- a/resources/NBTest/NBTest_051_CPCBalancer.py
+++ b/resources/NBTest/NBTest_051_CPCBalancer.py
@@ -15,11 +15,11 @@
 # ---
 
 # +
-from fastlane_bot.tools.cpc import ConstantProductCurve as CPC
+from fastlane_bot.tools.cpc import ConstantProductCurve as CPC, CurveBase
 from fastlane_bot.testing import *
+# from flbtools.cpc import ConstantProductCurve as CPC, CurveBase
+# from flbtesting import *
 
-#from flbtools.cpc import ConstantProductCurve as CPC
-#from flbtesting import *
 from math import sqrt
 print("{0.__name__} v{0.__VERSION__} ({0.__DATE__})".format(CPC))
 # from fastlane_bot import __VERSION__
@@ -33,6 +33,10 @@
 c0 = CPC.from_xy(100, 200)
 assert c0.tknx == "TKNB"
 assert c0.tkny == "TKNQ"
+k0 = c0.invariant()
+assert iseq(k0, sqrt(100*200))
+k1, k2 = c0.invariant(include_target=True)
+assert iseq(k0, k1, k2)
 
 x,y,_ = c0.xyfromp_f(c0.p)
 xvec = c0.xvecfrompvec_f({c0.tknx: c0.p, c0.tkny: 1} )
@@ -40,6 +44,7 @@
 assert iseq(y, 200)
 assert iseq(xvec[c0.tknx], x)
 assert iseq(xvec[c0.tkny], y)
+assert iseq(c0.invariant(), c0.invariant(xvec))
 assert raises(c0.xvecfrompvec_f, {c0.tknx: c0.p} ).startswith("pvec must contain")
 assert raises(c0.xvecfrompvec_f, {c0.tkny: 1} ).startswith("pvec must contain")
 
@@ -54,6 +59,7 @@
 assert iseq(y, 244.9489742783178)
 assert iseq(xvec[c0.tknx], x)
 assert iseq(xvec[c0.tkny], y)
+assert iseq(c0.invariant(), c0.invariant(xvec))
 
 dx,dy,_ = c0.dxdyfromp_f(c0.p)
 dxvec = c0.dxvecfrompvec_f({c0.tknx: c0.p, c0.tkny: 1} )
@@ -76,6 +82,39 @@
 assert iseq(dxvec[c0.tknx], dx)
 assert iseq(dxvec[c0.tkny], dy)
 
+
+# ## CurveBase
+
+# Checking that `CurveBase` can only instantiate with all functions defined
+
+# +
+class CB1(CurveBase):
+    pass
+
+class CB2(CurveBase):
+    def dxvecfrompvec_f(self, pvec, *, ignorebounds=False):
+        pass
+
+class CB3(CurveBase):
+    def xvecfrompvec_f(self, pvec, *, ignorebounds=False):
+        pass
+
+class CB4(CurveBase):
+    def xvecfrompvec_f(self, pvec, *, ignorebounds=False):
+        pass
+    def dxvecfrompvec_f(self, pvec, *, ignorebounds=False):
+        pass
+    def invariant(self, xvec=None, *, include_target=False):
+        pass
+    
+assert raises(CB1).startswith("Can't instantiate abstract class")
+assert raises(CB2).startswith("Can't instantiate abstract class")
+assert raises(CB3).startswith("Can't instantiate abstract class")
+assert not raises(CB4)
+# -
+
+assert isinstance(CPC.from_xy(100, 200), CurveBase)
+
 # ## Constant product constructor
 
 c0 = CPC.from_xy(100, 200)
@@ -152,14 +191,18 @@
 assert c0.alpha == 0.5
 assert c0.eta == 1
 assert c0.constr == "xy"
+assert iseq(c0.invariant(), c0.kbar)
 assert c0.is_constant_product() == True
 c0
 
+
+
 c1 = CPC.from_xyal(100, 200)
 assert c1.constr == "xyal"
 assert c1.is_constant_product() == True
 assert c1 == c0
 assert c1.asdict()["alpha"] == 0.5
+assert iseq(c1.invariant(), c1.kbar)
 c1
 
 c2 = CPC.from_xyal(100, 200, alpha=0.25)
@@ -168,6 +211,7 @@
 assert c2.alpha == 0.25
 assert c2.asdict()["alpha"] == 0.25
 assert iseq(c2.eta, 0.25/0.75)
+assert iseq(c2.invariant(), c2.kbar)
 assert c2 != c0
 assert c2 != c1
 c2
@@ -178,6 +222,7 @@
 assert iseq(c3.alpha, 0.8)
 assert c3.asdict()["alpha"] == 0.8
 assert iseq(c3.eta, 0.8/0.2)
+assert iseq(c3.invariant(), c3.kbar)
 assert c3 != c0
 assert c3 != c1
 assert c3 != c2