diff --git a/src/hncore/Digraph.zig b/src/hncore/Digraph.zig
index 29e5fdf..74dff4f 100644
--- a/src/hncore/Digraph.zig
+++ b/src/hncore/Digraph.zig
@@ -1,7 +1,7 @@
 const std = @import("std");
 
 /// A data type to store connections of nodes in directional-graph.
-pub fn Digraph(comptime T: type, comptime lessThanFn: LessThanFunc(T)) type {
+pub fn Container(comptime T: type, comptime lessThanFn: LessThanFunc(T)) type {
     return struct {
         ///
         pub const Node = T;
@@ -160,7 +160,7 @@ pub fn Digraph(comptime T: type, comptime lessThanFn: LessThanFunc(T)) type {
     };
 }
 
-/// A type of comparator function for the type T, which is to be passed as an argument of `Digraph()`.
+/// A type of comparator function for the type T, which is to be passed as an argument of `Container()`.
 pub fn LessThanFunc(comptime T: type) type {
     return fn (lhs: T, rhs: T) bool;
 }
@@ -179,15 +179,15 @@ pub fn lessThanFuncFor(comptime T: type) LessThanFunc(T) {
 }
 
 test "compile check for various types" {
-    _ = Digraph(u8,  lessThanFuncFor(u8));
-    _ = Digraph(u16, lessThanFuncFor(u16));
-    _ = Digraph(i8,  lessThanFuncFor(i8));
-    _ = Digraph(i16, lessThanFuncFor(i16));
-    _ = Digraph(*i8, lessThanFuncFor(*i8));
-    _ = Digraph(*anyopaque, lessThanFuncFor(*anyopaque));
+    _ = Container(u8,  lessThanFuncFor(u8));
+    _ = Container(u16, lessThanFuncFor(u16));
+    _ = Container(i8,  lessThanFuncFor(i8));
+    _ = Container(i16, lessThanFuncFor(i16));
+    _ = Container(*i8, lessThanFuncFor(*i8));
+    _ = Container(*anyopaque, lessThanFuncFor(*anyopaque));
 }
 test "check if connected" {
-    const Sut = Digraph(u8, lessThanFuncFor(u8));
+    const Sut = Container(u8, lessThanFuncFor(u8));
 
     const map = [_]Sut.Conn {
         .{ .from = 3, .to = 0, },
@@ -214,7 +214,7 @@ test "check if connected" {
     try std.testing.expect(!sut.isConnected(2, 1));
 }
 test "make new connection" {
-    const Sut = Digraph(u8, lessThanFuncFor(u8));
+    const Sut = Container(u8, lessThanFuncFor(u8));
 
     var sut = try Sut.init(std.testing.allocator, &.{});
     defer sut.deinit();
@@ -230,7 +230,7 @@ test "make new connection" {
     try std.testing.expect(!sut.isConnected(1, 3));
 }
 test "making an existing connection fails" {
-    const Sut = Digraph(u8, lessThanFuncFor(u8));
+    const Sut = Container(u8, lessThanFuncFor(u8));
 
     const map = [_]Sut.Conn {
         .{ .from = 0, .to = 1, },
@@ -242,7 +242,7 @@ test "making an existing connection fails" {
     try std.testing.expectError(Sut.Error.AlreadyConnected, sut.connect(0, 1));
 }
 test "disconnect an existing connection" {
-    const Sut = Digraph(u8, lessThanFuncFor(u8));
+    const Sut = Container(u8, lessThanFuncFor(u8));
 
     const map = [_]Sut.Conn {
         .{ .from = 0, .to = 1, },
@@ -258,7 +258,7 @@ test "disconnect an existing connection" {
     try std.testing.expect(!sut.isConnected(2, 3));
 }
 test "disconnecting a missing connection fails" {
-    const Sut = Digraph(u8, lessThanFuncFor(u8));
+    const Sut = Container(u8, lessThanFuncFor(u8));
 
     var sut = try Sut.init(std.testing.allocator, &.{});
     defer sut.deinit();
@@ -267,7 +267,7 @@ test "disconnecting a missing connection fails" {
     try std.testing.expectError(Sut.Error.NotConnected, sut.disconnect(1, 0));
 }
 test "chaotic operation" {
-    const Sut = Digraph(u16, lessThanFuncFor(u16));
+    const Sut = Container(u16, lessThanFuncFor(u16));
 
     var sut = try Sut.init(std.testing.allocator, &.{});
     defer sut.deinit();
diff --git a/src/hncore/Node.zig b/src/hncore/Node.zig
index 75b58a7..009dbdd 100644
--- a/src/hncore/Node.zig
+++ b/src/hncore/Node.zig
@@ -1,29 +1,27 @@
 const std = @import("std");
 
 ///
-pub const Node = struct {
-    /// unique and immutable integer
-    id: usize,
+/// unique and immutable integer
+id: usize,
 
-    /// summary text of this node
-    summary: []const u8,
+/// summary text of this node
+summary: []const u8,
 
-    ///
-    pub fn init(alloc: std.mem.Allocator, id: usize, summary: []const u8) !Node {
-        return .{
-            .id        = id,
-            .summary   = try alloc.dupe(u8, summary),
-        };
-    }
-    /// pass the same allocator as init() call
-    pub fn deinit(self: *@This(), alloc: std.mem.Allocator) void {
-        alloc.free(self.summary);
-    }
-};
+///
+pub fn init(alloc: std.mem.Allocator, id: usize, summary: []const u8) !@This() {
+    return .{
+        .id        = id,
+        .summary   = try alloc.dupe(u8, summary),
+    };
+}
+/// pass the same allocator as init() call
+pub fn deinit(self: *@This(), alloc: std.mem.Allocator) void {
+    alloc.free(self.summary);
+}
 
 test "serialize" {
     const alloc = std.testing.allocator;
-    var   node  = try Node.init(alloc, 0, "helloworld");
+    var   node  = try init(alloc, 0, "helloworld");
     defer node.deinit(alloc);
 
     var json = std.ArrayList(u8).init(alloc);