Section 193.2009 - Rules of regulatory construction(a) As used in this part:(1)Includes means including but not limited to;(2)May means is permitted to or is authorized to;(3)May not means is not permitted to or is not authorized to; and(4)Shall or must is used in the mandatory and imperative sense.(b) In this part: (1) Words importing the singular include the plural; and(2) Words importing the plural include the singular.45 FR 9203, Feb. 11, 1980, as amended by Amdt. 193-1, 45 FR 57418, Aug. 28, 1980; Amdt. 193-2, 45 FR 70404, Oct. 23, 1980; Amdt. 193-10, 61 FR 18517, Apr. 26, 1996; Amdt. 193-17, 65 FR 10958 , Mar. 1, 2000; 68 FR 11749 , Mar. 12, 2003; 70 FR 11140 , Mar. 8, 2005