DES - Definition of 'Feasible Event Sequence'

Feasible Event Sequence:

The event sequence $\{e_1,e_2,e_3,...\}$ is feasible for the state automaton ($\mathcal{E}$, $\mathcal{X}$, $\Gamma$, $f$, $x_0$) if $e_k\in \Gamma (x_{k-1})$ for all $k=1,2,3,...$

• If $e_k\notin \Gamma (x_{k-1})$ for some index k, the simulation returns an error.

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Translation:

If the sequence of events is not done right, then when simulating it, an event does occur but given the model of the system (which we suppose it is done right) it couldn’t. So the system doesn’t know at which state to go. $\Rightarrow$ The sequence of events is defined as unfeasible. $\Rightarrow$ And the system is said to be stuck in a singularity.

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~Example: Queuing system (cont’d)

The system it refers to is given here.