diff --git a/tests/guessnumber.d b/tests/guessnumber.d
new file mode 100644
index 0000000..45b470a
--- /dev/null
+++ b/tests/guessnumber.d
@@ -0,0 +1,31 @@
+import std.stdio, std.random, std.typecons, std.conv, std.string,
+       std.range;
+ 
+void main() {
+    immutable interval = tuple(1, 100);
+    writefln("Guess my target number that is between " ~
+             "%d and %d (inclusive).\n", interval[]);
+    immutable target = uniform!"[]"(interval[]);
+ 
+    foreach (immutable i; sequence!q{n}) {
+        writef("Your guess #%d: ", i + 1);
+        immutable txt = stdin.readln.strip;
+ 
+        Nullable!int answer;
+        try {
+            answer = txt.to!int;
+        } catch (ConvException e) {
+            writefln("  I don't understand your input '%s'", txt);
+            continue;
+        }
+        if (answer < interval[0] || answer > interval[1]) {
+            writeln("  Out of range!");
+            continue;
+        }
+        if (answer == target) {
+            writeln("  Well guessed.");
+            break;
+        }
+        writeln(answer < target ? "  Too low." : "  Too high.");
+    }
+}
diff --git a/tests/guessnumber.d.ref b/tests/guessnumber.d.ref
new file mode 100644
index 0000000..9ff51c1
--- /dev/null
+++ b/tests/guessnumber.d.ref
@@ -0,0 +1,36 @@
+import std.stdio, std.random, std.typecons, std.conv, std.string, std.range;
+
+void main()
+{
+    immutable interval = tuple(1, 100);
+    writefln("Guess my target number that is between "
+        ~ "%d and %d (inclusive).\n",
+        interval[]);
+    immutable target = uniform!"[]"(interval[]);
+    foreach (immutable i; sequence!q{n})
+    {
+        writef("Your guess #%d: ", i + 1);
+        immutable txt = stdin.readln.strip;
+        Nullable!int answer;
+        try
+        {
+            answer = txt.to!int;
+        }
+        catch(ConvException e)
+        {
+            writefln("  I don't understand your input '%s'", txt);
+            continue;
+        }
+        if (answer < interval[0] || answer > interval[1])
+        {
+            writeln("  Out of range!");
+            continue;
+        }
+        if (answer == target)
+        {
+            writeln("  Well guessed.");
+            break;
+        }
+        writeln(answer < target ? "  Too low.":"  Too high.");
+    }
+}
diff --git a/tests/heronian.d b/tests/heronian.d
new file mode 100644
index 0000000..ffe6334
--- /dev/null
+++ b/tests/heronian.d
@@ -0,0 +1,45 @@
+import std.stdio, std.math, std.range, std.algorithm, std.numeric, std.traits, std.typecons;
+ 
+double hero(in uint a, in uint b, in uint c) pure nothrow @safe @nogc {
+    immutable s = (a + b + c) / 2.0;
+    immutable a2 = s * (s - a) * (s - b) * (s - c);
+    return (a2 > 0) ? a2.sqrt : 0.0;
+}
+ 
+bool isHeronian(in uint a, in uint b, in uint c) pure nothrow @safe @nogc {
+    immutable h = hero(a, b, c);
+    return h > 0 && h.floor == h.ceil;
+}
+ 
+T gcd3(T)(in T x, in T y, in T z) pure nothrow @safe @nogc {
+    return gcd(gcd(x, y), z);
+}
+ 
+void main() /*@safe*/ {
+    enum uint maxSide = 200;
+ 
+    // Sort by increasing area, perimeter, then sides.
+    //auto h = cartesianProduct!3(iota(1, maxSide + 1))
+    auto r = iota(1, maxSide + 1);
+    const h = cartesianProduct(r, r, r)
+              //.filter!({a, b, c} => ...
+              .filter!(t => t[0] <= t[1] && t[1] <= t[2] &&
+                            t[0] + t[1] > t[2] &&
+                            t[].gcd3 == 1 && t[].isHeronian)
+              .array
+              .schwartzSort!(t => tuple(t[].hero, t[].only.sum, t.reverse))
+              .release;
+ 
+    static void showTriangles(R)(R ts) @safe {
+        "Area Perimeter Sides".writeln;
+        foreach (immutable t; ts)
+            writefln("%3s %8d %3dx%dx%d", t[].hero, t[].only.sum, t[]);
+    }
+ 
+    writefln("Primitive Heronian triangles with sides up to %d: %d", maxSide, h.length);
+    "\nFirst ten when ordered by increasing area, then perimeter,then maximum sides:".writeln;
+    showTriangles(h.take(10));
+ 
+    "\nAll with area 210 subject to the previous ordering:".writeln;
+    showTriangles(h.filter!(t => t[].hero == 210));
+}
diff --git a/tests/heronian.d.ref b/tests/heronian.d.ref
new file mode 100644
index 0000000..f7334ff
--- /dev/null
+++ b/tests/heronian.d.ref
@@ -0,0 +1,48 @@
+import std.stdio, std.math, std.range, std.algorithm, std.numeric, std.traits,
+    std.typecons;
+
+double hero(in uint a, in uint b, in uint c) pure nothrow @safe@nogc
+{
+    immutable s = (a + b + c) / 2.0;
+    immutable a2 = s * (s - a) * (s - b) * (s - c);
+    return (a2 > 0) ? a2.sqrt : 0.0;
+}
+
+bool isHeronian(in uint a, in uint b, in uint c) pure nothrow @safe @nogc
+{
+    immutable h = hero(a, b, c);
+    return h > 0 && h.floor == h.ceil;
+}
+
+T gcd3(T)(in T x, in T y, in T z) pure nothrow @safe @nogc
+{
+    return gcd(gcd(x, y), z);
+}
+
+void main() /*@safe*/
+{
+    enum uint maxSide = 200;
+    // Sort by increasing area, perimeter, then sides.
+    //auto h = cartesianProduct!3(iota(1, maxSide + 1))
+    auto r = iota(1, maxSide + 1);
+    const h = cartesianProduct(r, r, r)
+        //.filter!({a, b, c} => ...
+        .filter!(t => t[0] <= t[1] && t[1] <= t[2] && t[0] + t[1] > t[2] &&
+                      t[].gcd3 == 1 && t[].isHeronian)
+        .array.schwartzSort!(t => tuple(t[].hero, t[].only.sum, t.reverse))
+        .release;
+
+    static void showTriangles(R)(R ts) @safe
+    {
+        "Area Perimeter Sides".writeln;
+        foreach (immutable t; ts)
+            writefln("%3s %8d %3dx%dx%d", t[].hero, t[].only.sum, t[]);
+    }
+
+    writefln("Primitive Heronian triangles with sides up to %d: %d", maxSide,
+        h.length);
+    "\nFirst ten when ordered by increasing area, then perimeter,then maximum sides:".writeln;
+    showTriangles(h.take(10));
+    "\nAll with area 210 subject to the previous ordering:".writeln;
+    showTriangles(h.filter!(t => t[].hero == 210));
+}
diff --git a/tests/higherorder.d b/tests/higherorder.d
new file mode 100644
index 0000000..56d2c35
--- /dev/null
+++ b/tests/higherorder.d
@@ -0,0 +1,9 @@
+int hof(int a, int b, int delegate(int, int) f) {
+    return f(a, b);
+}
+ 
+void main() {
+    import std.stdio;
+    writeln("Add: ", hof(2, 3, (a, b) => a + b));
+    writeln("Multiply: ", hof(2, 3, (a, b) => a * b));
+}
diff --git a/tests/higherorder.d.ref b/tests/higherorder.d.ref
new file mode 100644
index 0000000..be9b953
--- /dev/null
+++ b/tests/higherorder.d.ref
@@ -0,0 +1,12 @@
+int hof(int a, int b, int delegate(int, int) f)
+{
+    return f(a, b);
+}
+
+void main()
+{
+    import std.stdio;
+
+    writeln("Add: ", hof(2, 3, (a, b) => a + b));
+    writeln("Multiply: ", hof(2, 3, (a, b) => a * b));
+}