-\Citeauthor{steenvoorden_tophat_2022} distinguishes two instruments for \gls{TOP}: \gls{TOP} languages and \gls{TOP} engines.
-The language is the \emph{formal} language for specifying interactive systems.
-The engine is the software or hardware that executes these specifications as a ready-for-work application.
+%\Citeauthor{steenvoorden_tophat_2022} distinguishes two instruments for \gls{TOP}: \gls{TOP} languages and \gls{TOP} engines.
+%The language is the \emph{formal} language for specifying interactive systems.
+%The engine is the software or hardware that executes these specifications as a ready-for-work application.
+%Defining comparable semantics for the \gls{MTASK} language is in progress \citep{antonova_mtask_2022}.
+
+\subsection{Tierless programming}
+Both \gls{ITASK} and \imtask{} are so called tierless systems.
+Tierless programming is an entirely different development paradigm compared to traditional, tiered, programming.
+In tiered programming, every component\slash{}tier is separately developed, possibly in different programming languages and programming paradigms, and integrated in the system as a whole.
+On the one hand, it is an advantage to be able to choose the most suitable programming language for the specific tier.
+But on the other, it increases the amount of integration work that needs to be done and it may increase the semantic friction between the tiers.
+In contrast, tierless programming languages synthesise all tiers of a software stack from a single high-level specification.
+Hence, reducing the semantic friction, increasing the maintainability costs, and reducing the possibility for runtime errors.
+The term tierless programming originated from the web programming system Links \citep{cooper2006links}.
+In Links, code for each tier simultaneously checked by the compiler, and compiled to HTML and JavaScript for the web client and to SQL on the server to interact with the database system.
+The \gls{ITASK} system is a tierless system taking care of both the presentation and application layer (see \cref{fig:iot-layers}).
+When \gls{ITASK} is used in conjunction with \gls{MTASK}, all layers of an \gls{IOT} system can be programmed from a single source and hence they are a tierless \gls{IOT} system.