diff --git a/src/factor_graph.rs b/src/factor_graph.rs
index c46ceff..150a995 100644
--- a/src/factor_graph.rs
+++ b/src/factor_graph.rs
@@ -1,13 +1,14 @@
-use std::collections::HashMap;
 use std::f64;
-use std::ops;
-
-use log::*;
 
 use crate::gaussian::Gaussian;
-use crate::graph::{MessageArena, MessageId, VariableArena, VariableId};
 use crate::math;
 
+mod message;
+mod variable;
+
+pub use message::*;
+pub use variable::*;
+
 pub struct PriorFactor {
     id: MessageId,
     variable: VariableId,
@@ -126,10 +127,8 @@ impl SumFactor {
 
     fn internal_update(
         &self,
-        variable_arena: &mut VariableArena,
-        message_arena: &mut MessageArena,
-        variable: VariableId,
-        message: MessageId,
+        variable: &mut Gaussian,
+        message: &mut Gaussian,
         y: &[Gaussian],
         fy: &[Gaussian],
         a: &[f64],
@@ -151,10 +150,10 @@ impl SumFactor {
 
         let gaussian = Gaussian::from_pi_tau(new_pi, new_tau);
 
-        let old = message_arena[message];
+        let old = *message;
 
-        message_arena[message] = gaussian;
-        variable_arena[variable] = variable_arena[variable] / old * gaussian;
+        *message = gaussian;
+        *variable = *variable / old * gaussian;
     }
 
     pub fn update_sum(&self, variable_arena: &mut VariableArena, message_arena: &mut MessageArena) {
@@ -166,10 +165,8 @@ impl SumFactor {
             .unzip();
 
         self.internal_update(
-            variable_arena,
-            message_arena,
-            self.sum,
-            self.sum_msg,
+            &mut variable_arena[self.sum],
+            &mut message_arena[self.sum_msg],
             &y,
             &fy,
             &self.coeffs,
@@ -214,10 +211,8 @@ impl SumFactor {
             .unzip();
 
         self.internal_update(
-            variable_arena,
-            message_arena,
-            idx_term,
-            idx_term_msg,
+            &mut variable_arena[idx_term],
+            &mut message_arena[idx_term_msg],
             &y,
             &fy,
             &a,
diff --git a/src/graph/message.rs b/src/factor_graph/message.rs
similarity index 100%
rename from src/graph/message.rs
rename to src/factor_graph/message.rs
diff --git a/src/graph/variable.rs b/src/factor_graph/variable.rs
similarity index 100%
rename from src/graph/variable.rs
rename to src/factor_graph/variable.rs
diff --git a/src/graph.rs b/src/graph.rs
deleted file mode 100644
index 07b1388..0000000
--- a/src/graph.rs
+++ /dev/null
@@ -1,420 +0,0 @@
-mod message;
-mod variable;
-
-pub use message::*;
-pub use variable::*;
-
-/*
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
-pub struct FactorId(usize);
-
-pub struct Graph {
-    variables: VariableArena,
-    factors: Vec<Factor>,
-    messages: MessageArena,
-}
-
-impl Graph {
-    #[inline(always)]
-    pub fn add_variable(&mut self) -> VariableId {
-        self.variables.create()
-    }
-
-    pub fn add_factor(&mut self, factor: Factor) -> FactorId {
-        let idx = self.factors.len();
-        self.factors.push(factor);
-
-        FactorId(idx)
-    }
-}
-
-pub enum Factor {
-    Prior { gaussian: Gaussian },
-}
-*/
-// FACTORS
-
-/*
-pub struct PriorFactor {
-    id: usize,
-    variable: VariableId,
-    gaussian: Gaussian,
-}
-
-impl PriorFactor {
-    pub fn new(
-        variable_arena: &mut VariableArena,
-        id: usize,
-        variable: VariableId,
-        gaussian: Gaussian,
-    ) -> PriorFactor {
-        variable_arena[variable].attach_factor(id);
-
-        PriorFactor {
-            id,
-            variable,
-            gaussian,
-        }
-    }
-
-    pub fn start(&self, variable_arena: &mut VariableArena) {
-        debug!(
-            "Prior::down var={:?}, value={:?}",
-            self.variable.index, self.gaussian
-        );
-
-        variable_arena[self.variable].update_value(self.id, self.gaussian);
-    }
-}
-*/
-
-/*
-pub struct Variable {
-    value: Gaussian,
-    factors: HashMap<usize, Gaussian>,
-}
-
-impl Variable {
-    pub fn attach_factor(&mut self, factor: usize) {
-        self.factors.insert(factor, Gaussian::from_pi_tau(0.0, 0.0));
-    }
-
-    pub fn update_value(&mut self, factor: usize, value: Gaussian) -> f64 {
-        let old = self.factors[&factor];
-
-        self.factors.insert(factor, value * old / self.value);
-
-        let pi_delta = (self.value.pi() - value.pi()).abs();
-
-        let delta = if !pi_delta.is_finite() {
-            0.0
-        } else {
-            let pi_delta = pi_delta.sqrt();
-            let tau_delta = (self.value.tau() - value.tau()).abs();
-
-            if pi_delta > tau_delta {
-                pi_delta
-            } else {
-                tau_delta
-            }
-        };
-
-        self.value = value;
-
-        debug!("Variable::value old={:?}, new={:?}", old, value);
-
-        delta
-    }
-
-    pub fn get_value(&self) -> Gaussian {
-        self.value
-    }
-
-    pub fn get_message(&self, factor: usize) -> Gaussian {
-        self.factors[&factor]
-    }
-
-    pub fn update_message(&mut self, factor: usize, message: Gaussian) {
-        let old = self.factors[&factor];
-
-        self.factors.insert(factor, message);
-        self.value = self.value / old * message;
-
-        debug!("Variable::message old={:?}, new={:?}", old, message);
-    }
-}
-*/
-
-/*
-pub struct PriorFactor {
-    id: usize,
-    variable: VariableId,
-    gaussian: Gaussian,
-}
-
-impl PriorFactor {
-    pub fn new(
-        variable_arena: &mut VariableArena,
-        id: usize,
-        variable: VariableId,
-        gaussian: Gaussian,
-    ) -> PriorFactor {
-        variable_arena[variable].attach_factor(id);
-
-        PriorFactor {
-            id,
-            variable,
-            gaussian,
-        }
-    }
-
-    pub fn start(&self, variable_arena: &mut VariableArena) {
-        debug!(
-            "Prior::down var={:?}, value={:?}",
-            self.variable.index, self.gaussian
-        );
-
-        variable_arena[self.variable].update_value(self.id, self.gaussian);
-    }
-}
-
-pub struct LikelihoodFactor {
-    id: usize,
-    mean: VariableId,
-    value: VariableId,
-    variance: f64,
-}
-
-impl LikelihoodFactor {
-    pub fn new(
-        variable_arena: &mut VariableArena,
-        id: usize,
-        mean: VariableId,
-        value: VariableId,
-        variance: f64,
-    ) -> LikelihoodFactor {
-        variable_arena[mean].attach_factor(id);
-        variable_arena[value].attach_factor(id);
-
-        LikelihoodFactor {
-            id,
-            mean,
-            value,
-            variance,
-        }
-    }
-
-    pub fn update_mean(&self, variable_arena: &mut VariableArena) {
-        let (x, fx) = {
-            let variable = &variable_arena[self.value];
-
-            (variable.get_value(), variable.get_message(self.id))
-        };
-
-        let a = 1.0 / (1.0 + self.variance * (x.pi() - fx.pi()));
-        let gaussian = Gaussian::from_pi_tau(a * (x.pi() - fx.pi()), a * (x.tau() - fx.tau()));
-
-        debug!(
-            "Likelihood::up var={:?}, value={:?}",
-            self.mean.index, gaussian
-        );
-
-        variable_arena[self.mean].update_message(self.id, gaussian);
-    }
-
-    pub fn update_value(&self, variable_arena: &mut VariableArena) {
-        let (y, fy) = {
-            let variable = &variable_arena[self.mean];
-
-            (variable.get_value(), variable.get_message(self.id))
-        };
-
-        let a = 1.0 / (1.0 + self.variance * (y.pi() - fy.pi()));
-        let gaussian = Gaussian::from_pi_tau(a * (y.pi() - fy.pi()), a * (y.tau() - fy.tau()));
-
-        debug!(
-            "Likelihood::down var={:?}, value={:?}",
-            self.value.index, gaussian
-        );
-
-        variable_arena[self.value].update_message(self.id, gaussian);
-    }
-}
-
-pub struct SumFactor {
-    id: usize,
-    sum: VariableId,
-    terms: Vec<VariableId>,
-    coeffs: Vec<f64>,
-}
-
-impl SumFactor {
-    pub fn new(
-        variable_arena: &mut VariableArena,
-        id: usize,
-        sum: VariableId,
-        terms: Vec<VariableId>,
-        coeffs: Vec<f64>,
-    ) -> SumFactor {
-        variable_arena[sum].attach_factor(id);
-
-        for term in &terms {
-            variable_arena[*term].attach_factor(id);
-        }
-
-        SumFactor {
-            id,
-            sum,
-            terms,
-            coeffs,
-        }
-    }
-
-    fn internal_update(
-        &self,
-        variable_arena: &mut VariableArena,
-        variable: VariableId,
-        y: &[Gaussian],
-        fy: &[Gaussian],
-        a: &[f64],
-    ) {
-        let (sum_pi, sum_tau) =
-            a.iter()
-                .zip(y.iter().zip(fy.iter()))
-                .fold((0.0, 0.0f64), |(pi, tau), (a, (y, fy))| {
-                    let x = *y / *fy;
-
-                    let new_pi = a.powi(2) / x.pi();
-                    let new_tau = a * x.mu();
-
-                    (pi + new_pi, tau + new_tau)
-                });
-
-        let new_pi = 1.0 / sum_pi;
-        let new_tau = new_pi * sum_tau;
-
-        let gaussian = Gaussian::from_pi_tau(new_pi, new_tau);
-
-        if variable == self.sum {
-            debug!("Sum::down var={:?}, value={:?}", variable.index, gaussian);
-        } else {
-            debug!("Sum::up var={:?}, value={:?}", variable.index, gaussian);
-        }
-
-        variable_arena[variable].update_message(self.id, gaussian);
-    }
-
-    pub fn update_sum(&self, variable_arena: &mut VariableArena) {
-        let (y, fy): (Vec<_>, Vec<_>) = self
-            .terms
-            .iter()
-            .map(|term| {
-                let variable = &variable_arena[*term];
-
-                (variable.get_value(), variable.get_message(self.id))
-            })
-            .unzip();
-
-        self.internal_update(variable_arena, self.sum, &y, &fy, &self.coeffs);
-    }
-
-    pub fn update_term(&self, variable_arena: &mut VariableArena, index: usize) {
-        let idx_term = self.terms[index];
-        let idx_coeff = self.coeffs[index];
-
-        let a = self
-            .coeffs
-            .iter()
-            .enumerate()
-            .map(|(i, coeff)| {
-                if i == index {
-                    1.0 / idx_coeff
-                } else {
-                    -coeff / idx_coeff
-                }
-            })
-            .collect::<Vec<_>>();
-
-        let (y, fy): (Vec<_>, Vec<_>) = self
-            .terms
-            .iter()
-            .enumerate()
-            .map(|(i, term)| {
-                let variable_id = if i == index { self.sum } else { *term };
-                let variable = &variable_arena[variable_id];
-
-                (variable.get_value(), variable.get_message(self.id))
-            })
-            .unzip();
-
-        self.internal_update(variable_arena, idx_term, &y, &fy, &a);
-    }
-
-    pub fn update_all_terms(&self, variable_arena: &mut VariableArena) {
-        for i in 0..self.terms.len() {
-            self.update_term(variable_arena, i);
-        }
-    }
-}
-
-fn v_win(t: f64, e: f64) -> f64 {
-    math::pdf(t - e) / math::cdf(t - e)
-}
-
-fn w_win(t: f64, e: f64) -> f64 {
-    let vwin = v_win(t, e);
-
-    vwin * (vwin + t - e)
-}
-
-fn v_draw(t: f64, e: f64) -> f64 {
-    (math::pdf(-e - t) - math::pdf(e - t)) / (math::cdf(e - t) - math::cdf(-e - t))
-}
-
-fn w_draw(t: f64, e: f64) -> f64 {
-    let vdraw = v_draw(t, e);
-    let n = (vdraw * vdraw) + ((e - t) * math::pdf(e - t) + (e + t) * math::pdf(e + t));
-    let d = math::cdf(e - t) - math::cdf(-e - t);
-
-    n / d
-}
-
-pub struct TruncateFactor {
-    id: usize,
-    variable: VariableId,
-    epsilon: f64,
-    draw: bool,
-}
-
-impl TruncateFactor {
-    pub fn new(
-        variable_arena: &mut VariableArena,
-        id: usize,
-        variable: VariableId,
-        epsilon: f64,
-        draw: bool,
-    ) -> TruncateFactor {
-        variable_arena[variable].attach_factor(id);
-
-        TruncateFactor {
-            id,
-            variable,
-            epsilon,
-            draw,
-        }
-    }
-
-    pub fn update(&self, variable_arena: &mut VariableArena) -> f64 {
-        let (x, fx) = {
-            let variable = &variable_arena[self.variable];
-
-            (variable.get_value(), variable.get_message(self.id))
-        };
-
-        let c = x.pi() - fx.pi();
-        let d = x.tau() - fx.tau();
-
-        let sqrt_c = c.sqrt();
-
-        let t = d / sqrt_c;
-        let e = self.epsilon * sqrt_c;
-
-        let (v, w) = if self.draw {
-            (v_draw(t, e), w_draw(t, e))
-        } else {
-            (v_win(t, e), w_win(t, e))
-        };
-
-        let m_w = 1.0 - w;
-
-        let gaussian = Gaussian::from_pi_tau(c / m_w, (d + sqrt_c * v) / m_w);
-
-        debug!(
-            "Trunc::up var={:?}, value={:?}",
-            self.variable.index, gaussian
-        );
-
-        variable_arena[self.variable].update_value(self.id, gaussian)
-    }
-}
-*/
diff --git a/src/graph/distribution.rs b/src/graph/distribution.rs
deleted file mode 100644
index 9ee54c2..0000000
--- a/src/graph/distribution.rs
+++ /dev/null
@@ -1,42 +0,0 @@
-use std::marker::PhantomData;
-use std::ops;
-
-use crate::gaussian::Gaussian;
-
-pub struct DistributionArena<T> {
-    arena: Vec<Gaussian>,
-    _phantom: PhantomData<T>,
-}
-
-impl<T> DistributionArena<T>
-where
-    T: From<usize>,
-{
-    pub fn create(&mut self) -> T {
-        let idx = self.arena.len();
-
-        self.arena.push(Gaussian::from_pi_tau(0.0, 0.0));
-
-        idx.into()
-    }
-}
-
-impl<T> ops::Index<T> for DistributionArena<T>
-where
-    T: Into<usize>,
-{
-    type Output = Gaussian;
-
-    fn index(&self, id: T) -> &Self::Output {
-        &self.arena[id.into()]
-    }
-}
-
-impl<T> ops::IndexMut<T> for DistributionArena<T>
-where
-    T: Into<usize>,
-{
-    fn index_mut(&mut self, id: T) -> &mut Self::Output {
-        &mut self.arena[id.into()]
-    }
-}
diff --git a/src/lib.rs b/src/lib.rs
index 1c0dc73..6678aba 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -2,13 +2,11 @@
 
 mod factor_graph;
 mod gaussian;
-mod graph;
 mod math;
 mod matrix;
 
 use crate::factor_graph::*;
 use crate::gaussian::Gaussian;
-use crate::graph::{MessageArena, VariableArena};
 use crate::matrix::Matrix;
 
 /// Default initial mean of ratings.