message: relax restriction.
diff: @@ -22,7 +22,7 @@ pub trait MulAcc<A = Self, B = A> {
  /// Default for types which supports `mul_add`
  impl<N, A, B> MulAcc<A, B> for N
  where
  - for<'x, 'y> &'x A: Mul<&'y B, Output = N>,
  + for<'x> &'x A: Mul<&'x B, Output = N>,
  N: AddAssign<N>
  {
  fn mul_acc(&mut self, a: &A, b: &B) {
  