diff --git a/little_learner/src/auto_diff.rs b/little_learner/src/auto_diff.rs
index e32511f..539362c 100644
--- a/little_learner/src/auto_diff.rs
+++ b/little_learner/src/auto_diff.rs
@@ -145,13 +145,12 @@ impl<A, Tag> DifferentiableContents<A, Tag> {
 
     fn map_tag<Tag2, F>(&self, f: &mut F) -> DifferentiableContents<A, Tag2>
     where
-        F: FnMut(Tag) -> Tag2,
+        F: FnMut(&Tag) -> Tag2,
         A: Clone,
-        Tag: Clone,
     {
         match self {
             DifferentiableContents::Scalar(a, tag) => {
-                DifferentiableContents::Scalar((*a).clone(), f((*tag).clone()))
+                DifferentiableContents::Scalar((*a).clone(), f(tag))
             }
             DifferentiableContents::Vector(slice, rank) => {
                 DifferentiableContents::Vector(slice.iter().map(|x| x.map_tag(f)).collect(), *rank)
@@ -253,9 +252,8 @@ impl<A, Tag> DifferentiableTagged<A, Tag> {
 
     pub fn map_tag<Tag2, F>(&self, f: &mut F) -> DifferentiableTagged<A, Tag2>
     where
-        F: FnMut(Tag) -> Tag2,
+        F: FnMut(&Tag) -> Tag2,
         A: Clone,
-        Tag: Clone,
     {
         DifferentiableTagged {
             contents: self.contents.map_tag(f),
@@ -572,13 +570,12 @@ impl<A, Tag, const RANK: usize> RankedDifferentiableTagged<A, Tag, RANK> {
     }
 
     pub fn map_tag<Tag2, F>(
-        self: RankedDifferentiableTagged<A, Tag, RANK>,
+        self: &RankedDifferentiableTagged<A, Tag, RANK>,
         f: &mut F,
     ) -> RankedDifferentiableTagged<A, Tag2, RANK>
     where
         A: Clone,
-        F: FnMut(Tag) -> Tag2,
-        Tag: Clone,
+        F: FnMut(&Tag) -> Tag2,
     {
         RankedDifferentiableTagged {
             contents: DifferentiableTagged::map_tag(&self.contents, f),
diff --git a/little_learner/src/decider.rs b/little_learner/src/decider.rs
new file mode 100644
index 0000000..9dcbe6c
--- /dev/null
+++ b/little_learner/src/decider.rs
@@ -0,0 +1,68 @@
+use crate::auto_diff::RankedDifferentiableTagged;
+use crate::loss::dot;
+use crate::scalar::Scalar;
+use crate::traits::{NumLike, Zero};
+
+fn rectify<A>(x: A) -> A
+where
+    A: Zero + PartialOrd,
+{
+    if x < A::zero() {
+        A::zero()
+    } else {
+        x
+    }
+}
+
+fn linear<A, Tag1, Tag2>(
+    t: RankedDifferentiableTagged<A, Tag1, 1>,
+    theta0: RankedDifferentiableTagged<A, Tag2, 1>,
+    theta1: Scalar<A>,
+) -> Scalar<A>
+where
+    A: NumLike,
+{
+    dot(&theta0, &t) + theta1
+}
+
+pub fn relu<A, Tag1, Tag2>(
+    t: RankedDifferentiableTagged<A, Tag1, 1>,
+    theta0: RankedDifferentiableTagged<A, Tag2, 1>,
+    theta1: Scalar<A>,
+) -> Scalar<A>
+where
+    A: NumLike + PartialOrd,
+{
+    rectify(linear(t, theta0, theta1))
+}
+
+#[cfg(test)]
+mod test_decider {
+    use crate::auto_diff::RankedDifferentiable;
+    use crate::decider::{linear, relu};
+    use crate::not_nan::to_not_nan_1;
+    use crate::scalar::Scalar;
+    use ordered_float::NotNan;
+
+    #[test]
+    fn test_linear() {
+        let theta0 = RankedDifferentiable::of_slice(&to_not_nan_1([7.1, 4.3, -6.4]));
+        let theta1 = Scalar::make(NotNan::new(0.6).expect("not nan"));
+        let t = RankedDifferentiable::of_slice(&to_not_nan_1([2.0, 1.0, 3.0]));
+
+        let result = linear(t, theta0, theta1).real_part().into_inner();
+
+        assert!((result + 0.1).abs() < 0.000_000_01);
+    }
+
+    #[test]
+    fn test_relu() {
+        let theta0 = RankedDifferentiable::of_slice(&to_not_nan_1([7.1, 4.3, -6.4]));
+        let theta1 = Scalar::make(NotNan::new(0.6).expect("not nan"));
+        let t = RankedDifferentiable::of_slice(&to_not_nan_1([2.0, 1.0, 3.0]));
+
+        let result = relu(t, theta0, theta1).real_part().into_inner();
+
+        assert_eq!(result, 0.0);
+    }
+}
diff --git a/little_learner/src/lib.rs b/little_learner/src/lib.rs
index e0aa15e..35daaf9 100644
--- a/little_learner/src/lib.rs
+++ b/little_learner/src/lib.rs
@@ -3,6 +3,7 @@
 #![feature(array_methods)]
 
 pub mod auto_diff;
+pub mod decider;
 pub mod gradient_descent;
 pub mod hyper;
 pub mod loss;
diff --git a/little_learner/src/loss.rs b/little_learner/src/loss.rs
index 3e08e15..44d2eaf 100644
--- a/little_learner/src/loss.rs
+++ b/little_learner/src/loss.rs
@@ -3,7 +3,7 @@ use std::{
     ops::{Add, Mul, Neg},
 };
 
-use crate::auto_diff::Differentiable;
+use crate::auto_diff::{Differentiable, RankedDifferentiableTagged};
 use crate::{
     auto_diff::{DifferentiableTagged, RankedDifferentiable},
     scalar::Scalar,
@@ -50,6 +50,23 @@ where
     dot_unranked_tagged(x, y, |(), ()| ())
 }
 
+pub fn dot<A, Tag1, Tag2>(
+    x: &RankedDifferentiableTagged<A, Tag1, 1>,
+    y: &RankedDifferentiableTagged<A, Tag2, 1>,
+) -> Scalar<A>
+where
+    A: Mul<Output = A> + Sum + Clone + Add<Output = A> + Zero,
+{
+    // Much sadness - find a way to get rid of these clones
+    let x = x.map_tag(&mut |_| ());
+    let y = y.map_tag(&mut |_| ());
+    x.to_vector()
+        .iter()
+        .zip(y.to_vector().iter())
+        .map(|(x, y)| x.clone().to_scalar() * y.clone().to_scalar())
+        .sum()
+}
+
 fn squared_2<A, const RANK: usize>(
     x: &RankedDifferentiable<A, RANK>,
 ) -> RankedDifferentiable<A, RANK>
diff --git a/little_learner/src/scalar.rs b/little_learner/src/scalar.rs
index ebe5936..72ebc88 100644
--- a/little_learner/src/scalar.rs
+++ b/little_learner/src/scalar.rs
@@ -1,5 +1,6 @@
 use crate::traits::{Exp, One, Sqrt, Zero};
 use core::hash::Hash;
+use std::cmp::Ordering;
 use std::{
     collections::{hash_map::Entry, HashMap},
     fmt::Display,
@@ -237,6 +238,15 @@ where
     }
 }
 
+impl<A> PartialOrd for Scalar<A>
+where
+    A: PartialOrd + Clone,
+{
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        self.real_part().partial_cmp(other.real_part())
+    }
+}
+
 impl<A> Exp for Scalar<A>
 where
     A: Exp + Clone,