diff --git a/src/lib.rs b/src/lib.rs
index ca036ab..c13d168 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,6 +5,7 @@ pub mod display;
 pub mod domain;
 pub mod functions;
 pub mod mapping;
+pub mod signature;
 pub mod tensor;
 
 pub use display::{BoxedTensor, format_boxed};
@@ -15,10 +16,11 @@ pub use functions::{
     zeros,
 };
 pub use mapping::{
-    BoxedMapping, BoxedPowersetMapping, COO, Concat, Diagonal, EmptyMapping, HRectSignature,
-    IndexMapping, InvProjection, Permutation, Powerset, PowersetMapping, Projection, Signature,
-    Squeeze, Stride, Unsqueeze, Where,
+    BoxedMapping, BoxedPowersetMapping, COO, Concat, Diagonal, EmptyMapping, IndexMapping,
+    InvProjection, Permutation, Powerset, PowersetMapping, Projection, Squeeze, Stride, Unsqueeze,
+    Where,
 };
+pub use signature::{HRectSignature, Signature};
 pub use tensor::{
     Inf, InfReduction, JaggedTensor, LeftComposition, Physical, Product, ProductReduction,
     Reduction, ReductionTensor, RightComposition, Sum, SumReduction, Sup, SupReduction, Tensor,
diff --git a/src/mapping.rs b/src/mapping.rs
index 8619aaf..e05a246 100644
--- a/src/mapping.rs
+++ b/src/mapping.rs
@@ -3,6 +3,7 @@ use std::rc::Rc;
 
 use crate::display::BoxedTensor;
 use crate::domain::{Domain, HRect, JaggedDomain};
+use crate::signature::{HRectSignature, Signature};
 
 /// A set of indices, as returned by a `PowersetMapping`.
 pub type Powerset = HashSet<Vec<usize>>;
@@ -39,29 +40,6 @@ pub trait BoxedPowersetMapping: PowersetMapping {
     fn hrect(&self) -> &HRect;
 }
 
-/// The domain and codomain a mapping runs between.
-pub struct Signature<D: Domain, C: Domain> {
-    domain: D,
-    codomain: C,
-}
-
-impl<D: Domain, C: Domain> Signature<D, C> {
-    pub fn new(domain: D, codomain: C) -> Self {
-        Self { domain, codomain }
-    }
-
-    pub fn domain(&self) -> &D {
-        &self.domain
-    }
-
-    pub fn codomain(&self) -> &C {
-        &self.codomain
-    }
-}
-
-/// The signature of a mapping between two hyperrectangles.
-pub type HRectSignature = Signature<HRect, HRect>;
-
 /// What a mapping from a hyperrectangle has to provide. Implementing this rather
 /// than `IndexMapping` gets the domain accessors and printability below for
 /// free, whatever the codomain; a mapping over a domain that is not a hrect
@@ -557,7 +535,7 @@ impl HRectMapping for Projection {
 }
 
 /// The inverse of the projection dropping axis `dim`.
-/// e.g. with dim=1, f(m, p) = {[m n p]^T | n in [N]}
+/// e.g. with dim=1, f(m, p) = {[m n p]^T | n in \[N\]}
 pub struct InvProjection {
     signature: HRectSignature,
     dim: usize,
diff --git a/src/signature.rs b/src/signature.rs
new file mode 100644
index 0000000..ee653cd
--- /dev/null
+++ b/src/signature.rs
@@ -0,0 +1,26 @@
+//! The domain and codomain a mapping runs between.
+
+use crate::domain::{Domain, HRect};
+
+/// The domain and codomain a mapping runs between.
+pub struct Signature<D: Domain, C: Domain> {
+    domain: D,
+    codomain: C,
+}
+
+impl<D: Domain, C: Domain> Signature<D, C> {
+    pub fn new(domain: D, codomain: C) -> Self {
+        Self { domain, codomain }
+    }
+
+    pub fn domain(&self) -> &D {
+        &self.domain
+    }
+
+    pub fn codomain(&self) -> &C {
+        &self.codomain
+    }
+}
+
+/// The signature of a mapping between two hyperrectangles.
+pub type HRectSignature = Signature<HRect, HRect>;