diff -r 6f22e4d277b4 -r 9b782aa6b452 src/direct_product.rs
--- a/src/direct_product.rs	Thu May 01 01:25:27 2025 -0500
+++ b/src/direct_product.rs	Thu May 01 01:31:25 2025 -0500
@@ -39,32 +39,6 @@
     }
 }
 
-macro_rules! impl_assignop {
-    (($a : ty, $b : ty), $trait : ident, $fn : ident, $refr:ident) => {
-        impl_assignop!(@doit: $a, $b,
-                              $trait, $fn;
-                              maybe_lifetime!($refr, &'r Pair<Ai,Bi>),
-                              (maybe_lifetime!($refr, &'r Ai),
-                               maybe_lifetime!($refr, &'r Bi));
-                              $refr);
-    };
-    (@doit: $a : ty, $b : ty,
-            $trait:ident, $fn:ident;
-            $in:ty, ($ain:ty, $bin:ty);
-            $refr:ident) => {
-        impl<'r, Ai, Bi> $trait<$in>
-        for Pair<$a,$b>
-        where $a: $trait<$ain>,
-              $b: $trait<$bin> {
-            #[inline]
-            fn $fn(&mut self, y : $in) -> () {
-                self.0.$fn(maybe_ref!($refr, y.0));
-                self.1.$fn(maybe_ref!($refr, y.1));
-            }
-        }
-    }
-}
-
 // macro_rules! impl_scalarop {
 //     (($a : ty, $b : ty), $field : ty, $trait : ident, $fn : ident, $refl:ident) => {
 //         impl_scalarop!(@doit: $field,
@@ -250,16 +224,46 @@
     };
 }
 
+macro_rules! impl_binary_mut {
+    ($trait:ident, $fn:ident) => {
+        impl<'a, A, B, C, D> $trait<Pair<C, D>> for Pair<A, B>
+        where
+            A: $trait<C>,
+            B: $trait<D>,
+        {
+            fn $fn(&mut self, Pair(c, d): Pair<C, D>) {
+                let Pair(ref mut a, ref mut b) = self;
+                a.$fn(c);
+                b.$fn(d);
+            }
+        }
+
+        impl<'a, 'b, A, B, C, D> $trait<&'b Pair<C, D>> for Pair<A, B>
+        where
+            A: $trait<&'b C>,
+            B: $trait<&'b D>,
+        {
+            fn $fn(&mut self, Pair(ref c, ref d): &'b Pair<C, D>) {
+                let Pair(ref mut a, ref mut b) = self;
+                a.$fn(c);
+                b.$fn(d);
+            }
+        }
+    };
+}
+
 impl_binary!(Add, add);
 impl_binary!(Sub, sub);
+impl_binary_mut!(AddAssign, add_assign);
+impl_binary_mut!(SubAssign, sub_assign);
 
 #[macro_export]
 macro_rules! impl_pair_vectorspace_ops {
     (($a:ty, $b:ty), $field:ty) => {
         //impl_pair_vectorspace_ops!(@binary, ($a, $b), Add, add);
         //impl_pair_vectorspace_ops!(@binary, ($a, $b), Sub, sub);
-        impl_pair_vectorspace_ops!(@assign, ($a, $b), AddAssign, add_assign);
-        impl_pair_vectorspace_ops!(@assign, ($a, $b), SubAssign, sub_assign);
+        //impl_pair_vectorspace_ops!(@assign, ($a, $b), AddAssign, add_assign);
+        //impl_pair_vectorspace_ops!(@assign, ($a, $b), SubAssign, sub_assign);
         // impl_pair_vectorspace_ops!(@scalar, ($a, $b), $field, Mul, mul);
         // impl_pair_vectorspace_ops!(@scalar, ($a, $b), $field, Div, div);
         // Compiler overflow
@@ -275,10 +279,6 @@
         impl_binop!(($a, $b), $trait, $fn, noref, ref);
         impl_binop!(($a, $b), $trait, $fn, noref, noref);
     };
-    (@assign, ($a : ty, $b : ty), $trait : ident, $fn :ident) => {
-        impl_assignop!(($a, $b), $trait, $fn, ref);
-        impl_assignop!(($a, $b), $trait, $fn, noref);
-    };
     (@scalar, ($a : ty, $b : ty), $field : ty, $trait : ident, $fn :ident) => {
         impl_scalarop!(($a, $b), $field, $trait, $fn, ref);
         impl_scalarop!(($a, $b), $field, $trait, $fn, noref);