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Acceptor for Ada identifiers

In Ada, an identifier consists of a letter followed by any number of letters, digits, and underlines. However, the identifier may not end in an underline or have two underlines in a row.

Here is an automaton to recognize Ada identifiers.

M = (Q, , , q0, F), where

Q is {q0, q1, q2, q3},
is {letter, digit, underline},

is given by

(q0, letter)    = q1        (q1, letter)    = q1
(q0, digit)     = q3        (q1, digit)     = q1
(q0, underline) = q3        (q1, underline) = q2

(q2, letter)    = q1        (q3, letter)    = q3
(q2, digit)     = q1        (q3, digit)     = q3
(q2, underline) = q3        (q3, underline) = q3

q0 Q is the initial state,
{q1} Q is a set of final states.