diff --git a/iface/CMakeLists.txt b/iface/CMakeLists.txt
index 3c5a247..c010c9d 100644
--- a/iface/CMakeLists.txt
+++ b/iface/CMakeLists.txt
@@ -15,6 +15,9 @@ target_sources(nf7_iface
     common/observer.hh
     common/task.hh
     common/value.hh
+    subsys/interface.hh
+    env.hh
+    lambda.hh
     version.hh
 )
 
diff --git a/iface/env.hh b/iface/env.hh
new file mode 100644
index 0000000..b01a7a7
--- /dev/null
+++ b/iface/env.hh
@@ -0,0 +1,11 @@
+// No copyright
+#pragma once
+
+#include "iface/common/container.hh"
+#include "iface/subsys/interface.hh"
+
+namespace nf7 {
+
+using Env = Container<subsys::Interface>;
+
+}  // namespace nf7
diff --git a/iface/lambda.hh b/iface/lambda.hh
new file mode 100644
index 0000000..a294280
--- /dev/null
+++ b/iface/lambda.hh
@@ -0,0 +1,40 @@
+// No copyright
+#pragma once
+
+#include <memory>
+#include <span>
+#include <utility>
+#include <vector>
+
+#include "iface/common/dealer.hh"
+#include "iface/common/value.hh"
+
+namespace nf7 {
+
+class Lambda {
+ public:
+  Lambda() = delete;
+  Lambda(std::vector<std::shared_ptr<Taker<Value>>>&& takers,
+         std::vector<std::shared_ptr<Maker<Value>>>&& makers) noexcept
+      : takers_(std::move(takers)), makers_(makers) {
+  }
+  virtual ~Lambda() = default;
+
+  Lambda(const Lambda&) = delete;
+  Lambda(Lambda&&) = delete;
+  Lambda& operator=(const Lambda&) = delete;
+  Lambda& operator=(Lambda&&) = delete;
+
+  std::span<const std::shared_ptr<Taker<Value>>> takers() const noexcept {
+    return takers_;
+  }
+  std::span<const std::shared_ptr<Maker<Value>>> makers() const noexcept {
+    return makers_;
+  }
+
+ private:
+  std::vector<std::shared_ptr<Taker<Value>>> takers_;
+  std::vector<std::shared_ptr<Maker<Value>>> makers_;
+};
+
+}  // namespace nf7
diff --git a/iface/subsys/interface.hh b/iface/subsys/interface.hh
new file mode 100644
index 0000000..8212db2
--- /dev/null
+++ b/iface/subsys/interface.hh
@@ -0,0 +1,24 @@
+// No copyright
+#pragma once
+
+namespace nf7::subsys {
+
+class Interface {
+ public:
+  Interface() = delete;
+  explicit Interface(const char* name) : name_(name) { }
+  virtual ~Interface() = default;
+
+  Interface(const Interface&) = delete;
+  Interface(Interface&&) = delete;
+  Interface& operator=(const Interface&) = delete;
+  Interface& operator=(Interface&&) = delete;
+
+  const char* name() const noexcept { return name_; }
+
+ private:
+  const char* name_;
+};
+
+
+}  // namespace nf7::subsys