In this chapter:
(1) "Attack" means any action or series of actions taken by an enemy of the United States resulting in substantial damage or injury to persons or property in this state whether by sabotage, bombs, missiles, shellfire, or atomic, radiological, chemical, bacteriological, or biological means or by other weapons or methods.
(2) "Unavailable" means dead or unable for physical, mental, or legal reasons to exercise the powers and discharge the duties of a legislator, whether or not the absence or inability would give rise to a vacancy under existing constitutional or statutory provisions.