message: Implement additive monoid
diff: @@ -993,6 +993,8 @@ mod alga_impls {
  }
  impl<N: Copy + Num, I: SpIndex> AbstractSemigroup<Additive> for CsVecI<N, I> {}
  +
  + impl<N: Copy + Num, I: SpIndex> AbstractMonoid<Additive> for CsVecI<N, I> {}
  }
  #[cfg(test)]
  