From 184a4de8df0ea3dc79ba672c363e0afa2bb30118 Mon Sep 17 00:00:00 2001
From: Robin Leroy <egg.robin.leroy@gmail.com>
Date: Sat, 23 Mar 2024 22:21:57 +0100
Subject: [PATCH 1/2] ambiguity

---
 quantities/concepts.hpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/quantities/concepts.hpp b/quantities/concepts.hpp
index 2b46b19bbf..6419da00dd 100644
--- a/quantities/concepts.hpp
+++ b/quantities/concepts.hpp
@@ -49,9 +49,12 @@ concept affine_space = requires(A x, A y) {
 template<typename V>
 concept real_affine_space = affine_space<V, double>;
 
+// std::integral || std::floating_point rather than
+// std::convertible_to<double, T> because
+// the former introduces ambiguities on Sign * Vector.
 template<typename T>
 concept convertible_to_quantity =
-    std::convertible_to<T, double> ||
+    std::integral<T> || std::floating_point<T> ||
     is_instance_of_v<Quantity, std::remove_cvref_t<T>>;
 
 }  // namespace internal

From 27e38721cc5aaa996a118329bd2e76ea772c515a Mon Sep 17 00:00:00 2001
From: Robin Leroy <egg.robin.leroy@gmail.com>
Date: Sat, 23 Mar 2024 22:22:21 +0100
Subject: [PATCH 2/2] alphabetize

---
 quantities/concepts.hpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/quantities/concepts.hpp b/quantities/concepts.hpp
index 6419da00dd..3fb5de6853 100644
--- a/quantities/concepts.hpp
+++ b/quantities/concepts.hpp
@@ -61,9 +61,9 @@ concept convertible_to_quantity =
 
 using internal::additive_group;
 using internal::affine_space;
+using internal::convertible_to_quantity;
 using internal::real_affine_space;
 using internal::real_vector_space;
-using internal::convertible_to_quantity;
 using internal::vector_space;
 
 }  // namespace _concepts