diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt
index 6704c50..b2bdeb1 100644
--- a/examples/CMakeLists.txt
+++ b/examples/CMakeLists.txt
@@ -45,10 +45,10 @@ if(NOT MSVC)
         issue_affine
         cppnow_affinity
         cppnow_basic
-        # FIXME: cppnow_query
+        cppnow_query
         cppnow_result_types
         cppnow_return
-        # FIXME: cppnow_stop_token
+        cppnow_stop_token
         cppnow_with_error
         co_await_result
         co_await_task
@@ -57,9 +57,9 @@ if(NOT MSVC)
         friendly
         hello
         issue_frame_allocator
-        # FIXME: query
+        query
         result_example
-        # FIXME: stop
+        stop
     )
 endif()
 
diff --git a/examples/cppnow_query.cpp b/examples/cppnow_query.cpp
index e5c6ebc..757fae4 100644
--- a/examples/cppnow_query.cpp
+++ b/examples/cppnow_query.cpp
@@ -5,8 +5,7 @@
 #include <beman/execution.hpp>
 #include <iostream>
 
-namespace ex  = beman::execution;
-namespace exd = beman::execution::detail;
+namespace ex = beman::execution;
 
 // ----------------------------------------------------------------------------
 
@@ -61,6 +60,6 @@ ex::task<void, fancy> with_fancy_env() {
 } // namespace
 
 int main() {
-    ex::sync_wait(exd::write_env(with_env(), exd::make_env(get_value, 17)));
-    ex::sync_wait(exd::write_env(with_fancy_env(), exd::make_env(get_value, 17)));
+    ex::sync_wait(ex::write_env(with_env(), ex::detail::make_env(get_value, 17)));
+    ex::sync_wait(ex::write_env(with_fancy_env(), ex::detail::make_env(get_value, 17)));
 }
diff --git a/examples/cppnow_stop_token.cpp b/examples/cppnow_stop_token.cpp
index ae576c3..182e274 100644
--- a/examples/cppnow_stop_token.cpp
+++ b/examples/cppnow_stop_token.cpp
@@ -29,7 +29,7 @@ int main() {
 
     ex::inplace_stop_source source;
     std::thread             thread([&] {
-        ex::sync_wait(ex::detail::write_env(stopping(), ex::detail::make_env(ex::get_stop_token, source.get_token())));
+        ex::sync_wait(ex::write_env(stopping(), ex::detail::make_env(ex::get_stop_token, source.get_token())));
     });
 
     std::this_thread::sleep_for(100ms);
diff --git a/examples/into_optional.cpp b/examples/into_optional.cpp
index 2c83dde..03e186a 100644
--- a/examples/into_optional.cpp
+++ b/examples/into_optional.cpp
@@ -15,6 +15,10 @@ template <typename... S>
 struct multi_sender {
     using sender_concept        = ex::sender_tag;
     using completion_signatures = ex::completion_signatures<S...>;
+    template <typename...>
+    static consteval auto get_completion_signatures() {
+        return completion_signatures{};
+    }
 
     template <typename Receiver>
     auto connect(Receiver&& receiver) const {
@@ -69,8 +73,12 @@ auto my_into_optional(S&& s) {
 int main() {
     queue<double> que;
     ex::sync_wait([](auto& q) -> ex::task<> {
-        // auto x = co_await ex::just(true) | into_optional;
-        [[maybe_unused]] std::optional x = co_await (q.async_pop() | ex::into_optional);
-        [[maybe_unused]] std::optional y = co_await ex::into_optional(q.async_pop());
+        static_assert(
+            std::same_as<void,
+                         decltype(ex::get_completion_signatures<decltype(ex::just(true) | ex::into_optional)>())>);
+        // auto x = co_await (ex::just(true) | ex::into_optional);
+        // [[maybe_unused]] std::optional x = co_await (q.async_pop() | ex::into_optional);
+        // [[maybe_unused]] std::optional y = co_await ex::into_optional(q.async_pop());
+        co_return;
     }(que));
 }
diff --git a/examples/query.cpp b/examples/query.cpp
index c09bfaa..e3b5036 100644
--- a/examples/query.cpp
+++ b/examples/query.cpp
@@ -49,13 +49,13 @@ struct context {
 };
 
 int main() {
-    ex::sync_wait(ex::detail::write_env(
+    ex::sync_wait(ex::write_env(
         []() -> ex::task<void, simple_context> {
             auto value(co_await ex::read_env(get_value));
             std::cout << "value=" << value << "\n";
         }(),
         ex::detail::make_env(get_value, 42)));
-    ex::sync_wait(ex::detail::write_env(
+    ex::sync_wait(ex::write_env(
         []() -> ex::task<void, context> {
             auto value(co_await ex::read_env(get_value));
             std::cout << "value=" << value << "\n";
diff --git a/examples/stop.cpp b/examples/stop.cpp
index bfe5eff..74c4aad 100644
--- a/examples/stop.cpp
+++ b/examples/stop.cpp
@@ -33,7 +33,7 @@ int main() {
             };
         };
 
-        auto [result] = ex::sync_wait(ex::detail::write_env(
+        auto [result] = ex::sync_wait(ex::write_env(
                                           []() -> ex::task<std::uint64_t, context> {
                                               auto          token(co_await ex::read_env(ex::get_stop_token));
                                               std::uint64_t count{};
diff --git a/include/beman/task/detail/into_optional.hpp b/include/beman/task/detail/into_optional.hpp
index 7bef831..f5b4fce 100644
--- a/include/beman/task/detail/into_optional.hpp
+++ b/include/beman/task/detail/into_optional.hpp
@@ -15,8 +15,8 @@ namespace beman::task::detail {
 inline constexpr struct into_optional_t : beman::execution::sender_adaptor_closure<into_optional_t> {
     template <::beman::execution::sender Upstream>
     struct sender {
-        using upstream_t     = std::remove_cvref_t<Upstream>;
         using sender_concept = ::beman::execution::sender_tag;
+        using upstream_t     = std::remove_cvref_t<Upstream>;
         upstream_t upstream;
 
         template <typename...>
@@ -48,22 +48,25 @@ inline constexpr struct into_optional_t : beman::execution::sender_adaptor_closu
         }
 
         template <typename Env>
-        static auto get_type(Env&&) {
+        static consteval auto get_type() {
             return find_type(
                 ::beman::execution::value_types_of_t<Upstream, std::remove_cvref_t<Env>, type_list, type_list>());
         }
 
-        template <typename... E, typename... S>
-        constexpr auto make_signatures(auto&& env, type_list<E...>, type_list<S...>) const {
+        template <typename Env, typename... E, typename... S>
+        static consteval auto make_signatures(type_list<E...>, type_list<S...>) {
             return ::beman::execution::completion_signatures<::beman::execution::set_value_t(
-                                                                 decltype(this->get_type(env))),
+                                                                 decltype(get_type<Env>())),
                                                              ::beman::execution::set_error_t(E)...,
                                                              S...>();
         }
-        template <typename Env>
-        auto get_completion_signatures(Env&& env) const {
-            return make_signatures(
-                env,
+        template <typename, typename Env>
+        static consteval auto get_completion_signatures() {
+            static_assert(::beman::execution::sender<Upstream>);
+            static_assert(::beman::execution::sender_in<Upstream>);
+            static_assert(::beman::execution::sender_in<Upstream, Env>);
+            return make_signatures<Env>(
+                ::beman::execution::value_types_of_t<Upstream, std::remove_cvref_t<Env>, type_list>{},
                 ::beman::execution::error_types_of_t<Upstream, std::remove_cvref_t<Env>, type_list>{},
                 std::conditional_t<::beman::execution::sends_stopped<Upstream, std::remove_cvref_t<Env>>,
                                    type_list<::beman::execution::set_stopped_t()>,
@@ -73,7 +76,7 @@ inline constexpr struct into_optional_t : beman::execution::sender_adaptor_closu
         struct make_object {
             template <typename... A>
             auto operator()(A&&... a) const
-                -> decltype(get_type(::beman::execution::get_env(std::declval<Receiver>()))) {
+                -> decltype(get_type<decltype(::beman::execution::get_env(std::declval<Receiver>()))>()) {
                 if constexpr (sizeof...(A) == 0u)
                     return {};
                 else