diff --git a/gtsam/hybrid/GaussianMixture.cpp b/gtsam/hybrid/GaussianMixture.cpp
index 82d16226a..a5d06f04d 100644
--- a/gtsam/hybrid/GaussianMixture.cpp
+++ b/gtsam/hybrid/GaussianMixture.cpp
@@ -21,6 +21,7 @@
 #include <gtsam/base/utilities.h>
 #include <gtsam/discrete/DiscreteValues.h>
 #include <gtsam/hybrid/GaussianMixture.h>
+#include <gtsam/hybrid/GaussianMixtureFactor.h>
 #include <gtsam/inference/Conditional-inst.h>
 #include <gtsam/linear/GaussianFactorGraph.h>
 
@@ -128,6 +129,36 @@ void GaussianMixture::print(const std::string &s,
       });
 }
 
+/* ************************************************************************* */
+KeyVector GaussianMixture::continuousParents() const {
+  // Get all parent keys:
+  const auto range = parents();
+  KeyVector continuousParentKeys(range.begin(), range.end());
+  // Loop over all discrete keys:
+  for (const auto &discreteKey : discreteKeys()) {
+    const Key key = discreteKey.first;
+    // remove that key from continuousParentKeys:
+    continuousParentKeys.erase(std::remove(continuousParentKeys.begin(),
+                                           continuousParentKeys.end(), key),
+                               continuousParentKeys.end());
+  }
+  return continuousParentKeys;
+}
+
+/* ************************************************************************* */
+boost::shared_ptr<GaussianMixtureFactor> GaussianMixture::likelihood(
+    const VectorValues &frontals) const {
+  // TODO(dellaert): check that values has all frontals
+  const DiscreteKeys discreteParentKeys = discreteKeys();
+  const KeyVector continuousParentKeys = continuousParents();
+  const GaussianMixtureFactor::Factors likelihoods(
+      conditionals(), [&](const GaussianConditional::shared_ptr &conditional) {
+        return conditional->likelihood(frontals);
+      });
+  return boost::make_shared<GaussianMixtureFactor>(
+      continuousParentKeys, discreteParentKeys, likelihoods);
+}
+
 /* ************************************************************************* */
 std::set<DiscreteKey> DiscreteKeysAsSet(const DiscreteKeys &dkeys) {
   std::set<DiscreteKey> s;
diff --git a/gtsam/hybrid/GaussianMixture.h b/gtsam/hybrid/GaussianMixture.h
index a3393dbb0..672a886ad 100644
--- a/gtsam/hybrid/GaussianMixture.h
+++ b/gtsam/hybrid/GaussianMixture.h
@@ -29,6 +29,8 @@
 
 namespace gtsam {
 
+class GaussianMixtureFactor;
+
 /**
  * @brief A conditional of gaussian mixtures indexed by discrete variables, as
  * part of a Bayes Network. This is the result of the elimination of a
@@ -117,16 +119,6 @@ class GTSAM_EXPORT GaussianMixture
       const DiscreteKeys &discreteParents,
       const std::vector<GaussianConditional::shared_ptr> &conditionals);
 
-  /// @}
-  /// @name Standard API
-  /// @{
-
-  GaussianConditional::shared_ptr operator()(
-      const DiscreteValues &discreteValues) const;
-
-  /// Returns the total number of continuous components
-  size_t nrComponents() const;
-
   /// @}
   /// @name Testable
   /// @{
@@ -140,6 +132,22 @@ class GTSAM_EXPORT GaussianMixture
       const KeyFormatter &formatter = DefaultKeyFormatter) const override;
 
   /// @}
+  /// @name Standard API
+  /// @{
+
+  GaussianConditional::shared_ptr operator()(
+      const DiscreteValues &discreteValues) const;
+
+  /// Returns the total number of continuous components
+  size_t nrComponents() const;
+
+  /// Returns the continuous keys among the parents.
+  KeyVector continuousParents() const;
+
+  // Create a likelihood factor for a Gaussian mixture, return a Mixture factor
+  // on the parents.
+  boost::shared_ptr<GaussianMixtureFactor> likelihood(
+      const VectorValues &frontals) const;
 
   /// Getter for the underlying Conditionals DecisionTree
   const Conditionals &conditionals() const;
@@ -181,6 +189,7 @@ class GTSAM_EXPORT GaussianMixture
    * @return Sum
    */
   Sum add(const Sum &sum) const;
+  /// @}
 };
 
 /// Return the DiscreteKey vector as a set.
diff --git a/gtsam/hybrid/tests/testGaussianMixture.cpp b/gtsam/hybrid/tests/testGaussianMixture.cpp
index 5542d86a9..ed5771770 100644
--- a/gtsam/hybrid/tests/testGaussianMixture.cpp
+++ b/gtsam/hybrid/tests/testGaussianMixture.cpp
@@ -154,53 +154,16 @@ static GaussianMixture createSimpleGaussianMixture() {
 }
 
 /* ************************************************************************* */
-std::set<DiscreteKey> DiscreteKeysAsSet(const DiscreteKeys& dkeys) {
-  std::set<DiscreteKey> s;
-  s.insert(dkeys.begin(), dkeys.end());
-  return s;
-}
-
-// Get only the continuous parent keys as a KeyVector:
-KeyVector continuousParents(const GaussianMixture& gm) {
-  // Get all parent keys:
-  const auto range = gm.parents();
-  KeyVector continuousParentKeys(range.begin(), range.end());
-  // Loop over all discrete keys:
-  for (const auto& discreteKey : gm.discreteKeys()) {
-    const Key key = discreteKey.first;
-    // remove that key from continuousParentKeys:
-    continuousParentKeys.erase(std::remove(continuousParentKeys.begin(),
-                                           continuousParentKeys.end(), key),
-                               continuousParentKeys.end());
-  }
-  return continuousParentKeys;
-}
-
 // Create a test for continuousParents.
 TEST(GaussianMixture, ContinuousParents) {
   const GaussianMixture gm = createSimpleGaussianMixture();
-  const KeyVector continuousParentKeys = continuousParents(gm);
+  const KeyVector continuousParentKeys = gm.continuousParents();
   // Check that the continuous parent keys are correct:
   EXPECT(continuousParentKeys.size() == 1);
   EXPECT(continuousParentKeys[0] == X(0));
 }
 
 /* ************************************************************************* */
-// Create a likelihood factor for a Gaussian mixture, return a Mixture factor.
-GaussianMixtureFactor::shared_ptr likelihood(const GaussianMixture& gm,
-                                             const VectorValues& frontals) {
-  // TODO(dellaert): check that values has all frontals
-  const DiscreteKeys discreteParentKeys = gm.discreteKeys();
-  const KeyVector continuousParentKeys = continuousParents(gm);
-  const GaussianMixtureFactor::Factors likelihoods(
-      gm.conditionals(),
-      [&](const GaussianConditional::shared_ptr& conditional) {
-        return conditional->likelihood(frontals);
-      });
-  return boost::make_shared<GaussianMixtureFactor>(
-      continuousParentKeys, discreteParentKeys, likelihoods);
-}
-
 /// Check that likelihood returns a mixture factor on the parents.
 TEST(GaussianMixture, Likelihood) {
   const GaussianMixture gm = createSimpleGaussianMixture();
@@ -208,7 +171,7 @@ TEST(GaussianMixture, Likelihood) {
   // Call the likelihood function:
   VectorValues measurements;
   measurements.insert(Z(0), Vector1(0));
-  const auto factor = likelihood(gm, measurements);
+  const auto factor = gm.likelihood(measurements);
 
   // Check that the factor is a mixture factor on the parents.
   // Loop over all discrete assignments over the discrete parents: