(1) Write a formal description (e.g., REs) of the token patterns, a Design a state transition diagram (DFA) that describes the token patterns and (2) write a program to implement the diagram, or (3) write a table-driven implementation of DFA.

[1] read in' str' from L-R, 1 sym' at a time[2] in 1 of a finite No. ofState[3]4 each sym' it moves to a new state determined by its current state&the sym' read[4] str' is acptd or rejcted depending on the state of the machine after read the final sym'

what is the formal deffinition of finite automation (FA) M

finite set Q of states, finite alphabet Σ of input symbols, distinguished start state q1 ∈ Q, set of final states F ⊆ Q, and transition function δ: Q × Σ → Q that chooses a new state for M based on the current state, Q, and the current input symbol, Σ

Similar to the case of REs, we name a set of symbols letter = {a, b, c,..., z, A, B, C,..., Z} digit = {0,...,9} and replace their arcs by a single arc labelled letter Or digit (or simply d as in our example)