diff --git a/include/tug/BoundaryCondition.hpp b/include/tug/BoundaryCondition.hpp
index 32748d9..498d519 100644
--- a/include/tug/BoundaryCondition.hpp
+++ b/include/tug/BoundaryCondition.hpp
@@ -32,6 +32,7 @@ enum {
 
 /**
  * Defines the boundary condition type and according value.
+ * QUESTION: For what is the struct bc necessary?
  */
 typedef struct boundary_condition_s {
   bctype type;  /**< Type of the boundary condition */
@@ -197,6 +198,7 @@ private:
 
   enum { X_DIM, Y_DIM };
 
+// TODO combine the 'public' blocks
 public:
   /**
    * Returns the left/right boundary condition for 1D grid.
diff --git a/include/tug/Diffusion.hpp b/include/tug/Diffusion.hpp
index 66c3dda..52d4920 100644
--- a/include/tug/Diffusion.hpp
+++ b/include/tug/Diffusion.hpp
@@ -15,6 +15,8 @@ constexpr uint8_t MAX_ARR_SIZE = 3;
 
 /**
  * Defines grid dimensions and boundary conditions.
+ * QUESTION: why is TugGrid a separate struct? For conceptual reasons?
+ * why not combine TugGrid and TugInput?
  */
 typedef struct tug_grid_s {
   std::array<uint32_t, MAX_ARR_SIZE>