diff --git a/Examples/src/RKFSolver/ButcherRKF.hpp b/Examples/src/RKFSolver/ButcherRKF.hpp
index 9f6e9d84..f8a8bc66 100644
--- a/Examples/src/RKFSolver/ButcherRKF.hpp
+++ b/Examples/src/RKFSolver/ButcherRKF.hpp
@@ -9,6 +9,7 @@
 #define SRC_RK45_BUTCHERRKF_HPP_
 #include <algorithm>
 #include <array>
+#include <concepts>
 #include <numeric>
 namespace apsc
 {
@@ -97,6 +98,21 @@ template <unsigned int NSTAGES> struct ButcherArray
   }
 };
 
+template <typename B>
+concept ButcherArrayConcept = requires(B b) {
+                                b.A;
+                                b.b1;
+                                b.b2;
+                                b.c;
+                                b.order;
+                                {
+                                  b.implicit()
+                                  } -> std::same_as<bool>;
+                                {
+                                  B::Nstages()
+                                  } -> std::convertible_to<unsigned int>;
+                              };
+
 namespace RKFScheme
 {
   // SOME COMMON RK embedded schemes
diff --git a/Examples/src/RKFSolver/RKF.hpp b/Examples/src/RKFSolver/RKF.hpp
index 0369be9b..517aef30 100644
--- a/Examples/src/RKFSolver/RKF.hpp
+++ b/Examples/src/RKFSolver/RKF.hpp
@@ -49,7 +49,7 @@ template <RKFKind KIND> struct RKFResult
  * scheme shown in ButcherRKF.hpp
  * @tparam KIND The type of traits to be used: SCALAR, VECTOR, MATRIX
  */
-template <class B, RKFKind KIND = RKFKind::SCALAR>
+template <apsc::ButcherArrayConcept B, RKFKind KIND = RKFKind::SCALAR>
 class RKF : public RKFTraits<KIND>
 {
 public:
diff --git a/Examples/src/RKFSolver/main_rk45.cpp b/Examples/src/RKFSolver/main_rk45.cpp
index 1fd81a22..40a79b6d 100644
--- a/Examples/src/RKFSolver/main_rk45.cpp
+++ b/Examples/src/RKFSolver/main_rk45.cpp
@@ -33,7 +33,8 @@ main()
               << errorDesired << " Failed:" << solution.failed
               << " Estimated Error " << solution.estimatedError
               << "\n Contractions=" << solution.contractions
-              << " Expansions=" << solution.expansions;
+              << " Expansions=" << solution.expansions << " Total steps "
+              << solution.time.size();
     std::cout << std::endl;
 
     // auto solution = solver(t0,T, y0, h_init, errorDesired);
@@ -66,7 +67,8 @@ main()
               << " Failed:" << solution.failed << " Estimated Error "
               << solution.estimatedError
               << "\n Contractions=" << solution.contractions
-              << " Expansions=" << solution.expansions;
+              << " Expansions=" << solution.expansions << " Total steps "
+              << solution.time.size();
     std::cout << std::endl;
     ofstream file3("resultVDP.dat");
     file3 << solution;
@@ -97,7 +99,9 @@ main()
               << " Failed:" << solution.failed << " Estimated Error "
               << solution.estimatedError
               << "\n Contractions=" << solution.contractions
-              << " Expansions=" << solution.expansions;
+              << " Expansions=" << solution.expansions << " Total steps "
+              << solution.time.size();
+
     std::cout << std::endl;
     ofstream file3("resultstiff.dat");
     file3 << solution;