diff --git a/content/code/R/even_time_difference.R b/content/code/R/even_time_difference.R
new file mode 100644
index 0000000..6411f0a
--- /dev/null
+++ b/content/code/R/even_time_difference.R
@@ -0,0 +1,12 @@
+#' Check time to now even
+#'
+#' Checks whether time difference between now and given time in seconds is even
+#'
+#' @param seconds input time in whole seconds
+#'
+#' @return returns true or false
+check_time_to_now_even <- function(seconds) {
+  if(seconds < 0) stop('received negative input')
+  now <- as.integer(format(Sys.time(), '%s'))
+  return((seconds - now) %% 2 == 0)
+}
diff --git a/content/code/R/reactor_temperature_sol.R b/content/code/R/even_time_difference_sol.R
similarity index 100%
rename from content/code/R/reactor_temperature_sol.R
rename to content/code/R/even_time_difference_sol.R
diff --git a/content/code/R/reactor_temperature.R b/content/code/R/reactor_temperature.R
deleted file mode 100644
index 69b16cb..0000000
--- a/content/code/R/reactor_temperature.R
+++ /dev/null
@@ -1,16 +0,0 @@
-# reactor <- namespace::makeNamespace("reactor")
-# assign("max_temperature", 100, env = reactor)
-# namespaceExport(reactor, "max_temperature")
-
-#' Checks whether the temperature is above max_temperature
-#' and returns the status.
-#'
-#' @param temperature_celsius The temperature of the core
-#' @return 1 if the temperature is in range, otherwise 0
-check_reactor_temperature <- function(temperature_celsius) {
-  if (temperature_celsius > reactor::max_temperature)
-    status <- 1
-  else
-    status <- 0
-  status
-}
diff --git a/content/code/cpp/even_time_difference.cpp b/content/code/cpp/even_time_difference.cpp
new file mode 100644
index 0000000..687fdac
--- /dev/null
+++ b/content/code/cpp/even_time_difference.cpp
@@ -0,0 +1,11 @@
+#include <chrono>
+#include <stdexcept>
+
+/* Checks whether temperature is above max_temperature and returns a status. */
+bool check_time_to_now_even(int seconds) {
+	if(seconds<0){
+		throw std::runtime_error('received negative input');
+	}
+  auto now = std::chrono::system_clock::now().time_since_epoch();
+    return (std::chrono::duration_cast<std::chrono::seconds>(now).count()-seconds)%2 ==0;
+}
diff --git a/content/code/cpp/even_time_difference_sol.cpp b/content/code/cpp/even_time_difference_sol.cpp
new file mode 100644
index 0000000..5800fb8
--- /dev/null
+++ b/content/code/cpp/even_time_difference_sol.cpp
@@ -0,0 +1,54 @@
+// Changing variables included from headers (monkey patching) is not possible in
+// C++. Instead we refactor the function to make it pure.
+// Another way would be to use templates for dependency injection
+#include <catch2/catch.hpp>
+
+// Making it pure, probably renaming would be a good idea
+bool check_time_to_now_even(int seconds, int current_time) {
+  if (seconds < 0) {
+    throw std::runtime_error('received negative input');
+  }
+  return (current_time - seconds) % 2 == 0;
+}
+
+// Normal invocation
+auto now = std::chrono::system_clock::now().time_since_epoch();
+int current_time_seconds =
+    std::chrono::duration_cast<std::chrono::seconds>(now).count();
+check_time_to_now_even(4, current_time_seconds);
+
+TEST_CASE("Check time difference", "[reactor_state]") {
+  REQUIRE(check_time_to_now_even(1, 3) == true);
+  REQUIRE(check_time_to_now_even(4, 5) == false);
+}
+
+// using templates
+
+template <class CLOCK> bool check_time_to_now_even(int seconds) {
+  if (seconds < 0) {
+    throw std::runtime_error('received negative input');
+  }
+  int current_time = CLOCK.getNowSeconds();
+  return (current_time - seconds) % 2 == 0;
+}
+
+// Normal invocation
+class ChronoClock {
+
+  int getNowSeconds() {
+    auto now = std::chrono::system_clock::now().time_since_epoch();
+    return std::chrono::duration_cast<std::chrono::seconds>(now).count();
+  }
+};
+
+check_time_to_now_even<ChronoClock>(3);
+
+class TestClock {
+
+  int getNowSeconds() { return 3; }
+};
+
+TEST_CASE("Check time difference", "[reactor_state]") {
+  REQUIRE(check_time_to_now_even<TestClock>(3) == true);
+  REQUIRE(check_time_to_now_even<TestClock>(4) == false);
+}
\ No newline at end of file
diff --git a/content/code/cpp/reactor_temperature.cpp b/content/code/cpp/reactor_temperature.cpp
deleted file mode 100644
index cbbfee5..0000000
--- a/content/code/cpp/reactor_temperature.cpp
+++ /dev/null
@@ -1,15 +0,0 @@
-#include "constants.hpp"
-/* ^--- Defines the max_temperature constant as:
-* namespace constants {
-* constexpr double max_temperature = 100.0;
-* }
-*/
-
-enum class ReactorState : int { FINE, CRITICAL };
-
-/* Checks whether temperature is above max_temperature and returns a status. */
-ReactorState check_reactor_temperature(double temperature_celsius) {
-  return temperature_celsius > constants::max_temperature
-	     ? ReactorState::CRITICAL
-	     : ReactorState::FINE;
-}
diff --git a/content/code/cpp/reactor_temperature_sol.cpp b/content/code/cpp/reactor_temperature_sol.cpp
deleted file mode 100644
index 37a1cb6..0000000
--- a/content/code/cpp/reactor_temperature_sol.cpp
+++ /dev/null
@@ -1,9 +0,0 @@
-// Changing variables included from headers (monkey patching) is not possible in C++.
-#include <catch2/catch.hpp>
-
-#include "reactor.hpp"
-
-TEST_CASE("Check reactor state", "[reactor_state]") {
-  REQUIRE(check_reactor_temperature(99) == ReactorState::FINE);
-  REQUIRE(check_reactor_temperature(100) == ReactorState::FINE);
-  REQUIRE(check_reactor_temperature(101) == ReactorState::CRITICAL);
diff --git a/content/code/fortran/reactor_temperature.f90 b/content/code/fortran/even_time_difference.f90
similarity index 100%
rename from content/code/fortran/reactor_temperature.f90
rename to content/code/fortran/even_time_difference.f90
diff --git a/content/code/fortran/reactor_temperature_sol.f90 b/content/code/fortran/even_time_difference_sol.f90
similarity index 100%
rename from content/code/fortran/reactor_temperature_sol.f90
rename to content/code/fortran/even_time_difference_sol.f90
diff --git a/content/code/julia/reactor_temperature.jl b/content/code/julia/even_time_difference.jl
similarity index 100%
rename from content/code/julia/reactor_temperature.jl
rename to content/code/julia/even_time_difference.jl
diff --git a/content/code/julia/reactor_temperature_sol.jl b/content/code/julia/even_time_difference_sol.jl
similarity index 100%
rename from content/code/julia/reactor_temperature_sol.jl
rename to content/code/julia/even_time_difference_sol.jl
diff --git a/content/code/python/even_time_difference.py b/content/code/python/even_time_difference.py
new file mode 100644
index 0000000..22841b5
--- /dev/null
+++ b/content/code/python/even_time_difference.py
@@ -0,0 +1,10 @@
+import time
+def check_time_to_now_even(seconds):
+    """
+    Checks whether time difference between now and given time in seconds is even
+    """
+    if seconds < 0:
+        raise ValueError('received negative input')
+   
+    now=time.time()
+    return (seconds-now)%2 == 0
\ No newline at end of file
diff --git a/content/code/python/even_time_difference_sol.py b/content/code/python/even_time_difference_sol.py
new file mode 100644
index 0000000..d0b0b22
--- /dev/null
+++ b/content/code/python/even_time_difference_sol.py
@@ -0,0 +1,6 @@
+def test_check_time(monkeypatch):
+  def mocktime():
+    return 2
+  monkeypatch.setattr(time,"time",mocktime)
+  assert check_time_to_now_even(0) == 1
+  assert check_time_to_now_even(1) == 0
\ No newline at end of file
diff --git a/content/code/python/reactor_temperature.py b/content/code/python/reactor_temperature.py
deleted file mode 100644
index 7e998f5..0000000
--- a/content/code/python/reactor_temperature.py
+++ /dev/null
@@ -1,10 +0,0 @@
-def check_reactor_temperature(temperature_celsius):       """
-    Checks whether temperature is above max_temperature
-    and returns a status.
-    """
-    from reactor import max_temperature
-    if temperature_celsius > max_temperature:
-        status = 1
-    else:
-        status = 0
-    return status
diff --git a/content/code/python/reactor_temperature_sol.py b/content/code/python/reactor_temperature_sol.py
deleted file mode 100644
index d01317c..0000000
--- a/content/code/python/reactor_temperature_sol.py
+++ /dev/null
@@ -1,5 +0,0 @@
-def test_set_temp(monkeypatch):
-    monkeypatch.setattr(reactor, "max_temperature", 100)
-    assert check_reactor_temperature(99)  == 0
-    assert check_reactor_temperature(100) == 0   # boundary cases easily go wrong
-    assert check_reactor_temperature(101) == 1
diff --git a/content/test-design.md b/content/test-design.md
index bf2cf62..d62b514 100644
--- a/content/test-design.md
+++ b/content/test-design.md
@@ -337,45 +337,44 @@ This one is not easy to test because the function has an external dependency.
 
    ````{tab} Python
 
-      ```{literalinclude} code/python/reactor_temperature.py
+      ```{literalinclude} code/python/even_time_difference.py
       :language: Python
       ```
    ````
 
    ````{tab} C++
 
-      ```{literalinclude} code/cpp/reactor_temperature.cpp
+      ```{literalinclude} code/cpp/even_time_difference.cpp
       :language: c++
       ```
    ````
 
    ````{tab} R
 
-      ```{literalinclude} code/R/reactor_temperature.R
+      ```{literalinclude} code/R/even_time_difference.R
       :language: R
       ```
    ````
 
    ````{tab} Julia
 
-      ```{literalinclude} code/julia/reactor_temperature.jl
+      ```{literalinclude} code/julia/even_time_difference.jl
       :language: julia
       ```
    ````
 
    ````{tab} Fortran
 
-      ```{literalinclude} code/fortran/reactor_temperature.f90
+      ```{literalinclude} code/fortran/even_time_difference.f90
       :language: fortran
       ```
    ````
 `````
 
 ``````{solution}
-This function depends on the value of
-`reactor.max_temperature` so the function is not pure, so testing gets
-harder. You could use monkey patching to override the value of
-`max_temperature`, and test it with different values.  [Monkey
+This function depends on the current time, so the function is not pure, so testing gets
+harder. You could use monkey patching to replace the time function with another function
+, and test it with different values.  [Monkey
 patching](https://en.wikipedia.org/wiki/Monkey_patch) is the concept
 of artificially changing some other value.
 
@@ -385,35 +384,35 @@ A better solution would probably be to rewrite the function.
 
    ````{tab} Python
 
-      ```{literalinclude} code/python/reactor_temperature_sol.py
+      ```{literalinclude} code/python/even_time_difference_sol.py
       :language: Python
       ```
    ````
 
    ````{tab} C++
 
-      ```{literalinclude} code/cpp/reactor_temperature_sol.cpp
+      ```{literalinclude} code/cpp/even_time_difference_sol.cpp
       :language: c++
       ```
    ````
 
    ````{tab} R
 
-      ```{literalinclude} code/R/reactor_temperature_sol.R
+      ```{literalinclude} code/R/even_time_difference_sol.R
       :language: R
       ```
    ````
 
    ````{tab} Julia
 
-      ```{literalinclude} code/julia/reactor_temperature_sol.jl
+      ```{literalinclude} code/julia/even_time_difference_sol.jl
       :language: julia
       ```
    ````
 
    ````{tab} Fortran
 
-      ```{literalinclude} code/fortran/reactor_temperature_sol.f90
+      ```{literalinclude} code/fortran/even_time_difference_sol.f90
       :language: fortran
       ```
    ````