diff --git a/include/kyosu/types/impl/bessel/sb_ikn.hpp b/include/kyosu/types/impl/bessel/sb_ikn.hpp
index f09ee5e4..167733f8 100644
--- a/include/kyosu/types/impl/bessel/sb_ikn.hpp
+++ b/include/kyosu/types/impl/bessel/sb_ikn.hpp
@@ -59,13 +59,14 @@ namespace kyosu::_
   auto sb_i2n(N n, Z z, R & sis) noexcept
   {
     using e_t = as_real_type_t<Z>;
-    auto iton = [](N n){
-      if (n%4 == 0) return complex(eve::one(eve::as<e_t>()));
-      else if (n%4 == 1) return  complex(eve::zero(eve::as<e_t>()), eve::one(eve::as<e_t>()));
-      else if (n%4 == 2) return complex(eve::mone(eve::as<e_t>()));
-      else return complex(eve::zero(eve::as<e_t>()), eve::mone(eve::as<e_t>()));
+    auto riton = [](N n){
+      n =  n & N(3);
+      if (n == 0) return complex(eve::one(eve::as<e_t>()));
+      else if (n == 1) return  complex(eve::zero(eve::as<e_t>()), eve::mone(eve::as<e_t>()));
+      else if (n == 2) return complex(eve::mone(eve::as<e_t>()));
+      else return complex(eve::zero(eve::as<e_t>()), eve::one(eve::as<e_t>()));
     };
-    return rec(iton(n +1))*sph_bessel_yn(n,muli(z), sis);
+    return riton(n+1)*sph_bessel_yn(n,muli(z), sis);
   }
 
 
diff --git a/include/kyosu/types/impl/detail/cylseq.hpp b/include/kyosu/types/impl/detail/cylseq.hpp
deleted file mode 100644
index a9ae7bc2..00000000
--- a/include/kyosu/types/impl/detail/cylseq.hpp
+++ /dev/null
@@ -1,51 +0,0 @@
-//======================================================================================================================
-/*
-  Kyosu - Complex Without Complexes
-  Copyright : KYOSU Contributors & Maintainers
-  SPDX-License-Identifier: BSL-1.0
-*/
-//======================================================================================================================
-#pragma once
-
-namespace kyosu::_
-{
-
-  template<typename F, typename Z, eve::detail::range Ra>
-  void dispatch(eve::tag_of<kyosu::cyl_seq>, F f, size_t n, Z z, Ra & cbs) noexcept
-  {
-    std::cout << "icitte seq" << std::endl;
-    if constexpr(concepts::complex<Z>)
-    {
-      if constexpr(concepts::cayley_dickson<F>)
-        *std::begin(cbs) = f;
-      else
-        *std::begin(cbs) = f(n, z);
-      if (n == 0)
-        return;
-      else
-      {
-        auto rz = kyosu::rec(z);
-        EVE_ASSERT(cbs.size() >= n+1, "cbs has not room enough");
-        auto rs =kyosu::_:: R(n, z);
-        int i = n-1;
-
-        auto cur = std::rbegin(cbs);
-        *cur = f(n, z);
-        auto pred = cur++;
-        while (i >= 0)
-        {
-          *cur++ = *pred++*rs;
-          rs = 2*(i--)*rz-kyosu::rec(rs);
-        }
-      }
-    }
-    else
-    {
-      auto p = kyosu::pure(z);
-      auto az = kyosu::abs(p);
-      cyl_bessel_cbs(n, kyosu::complex(kyosu::real(z), az), cbs);
-      for(size_t i = 0; i <= n; ++i) cbs[i] = kyosu::real(cbs[i]) + kyosu::ipart(cbs[i])*kyosu::sign(p);
-    }
-  }
-
-}