155 (d) a Senator, the notice must be addressed to the president of the Senate; (e) a member of the National Assembly, the notice must be addressed to the Speaker; (f) a member of a provincial council, the notice must be addressed to the Provincial Governor; (g) a member of a metropolitan council, the notice must be addressed to the mayor of the province; (h) a member of a local authority, the notice must be addressed to the chief executive officer of the council. (2) A person’s resignation from an office established by this Constitution takes effect on the date or at the time indicated in the notice of resignation or, if no date or time is indicated, when the notice is received by the person to whom it is addressed or by anyone else who is authorised by that person to receive it. 18.25 Exercise of functions, etc. (1) A power, jurisdiction or right conferred by this Constitution may be exercised, and a duty imposed by this Constitution must be performed, whenever it is appropriate to do so. (2) All institutions established by this Constitution have all powers necessary for them to fulfil their objectives and exercise their functions. (3) Where a power, jurisdiction or right is conferred by this Constitution, any other powers or rights that are reasonably necessary or incidental to its exercise are impliedly conferred as well. 18.26 When person not regarded as holding public office For the purposes of this Constitution, persons are not to be regarded as holding public office solely on the ground that they receive a pension, half-pay, retirement pay or some other similar allowance in respect of previous service in a public office. 18.27 Quorum and effect of vacancies in constitutional bodies (1) A body established by or under this Constitution may act even if there are one or more vacancies in its membership, provided that the members of the body who authorise or perform the act are a quorum. (2) Unless this Constitution or a law regulating the proceedings of the body concerned makes some different provision, half the total membership of any body established by or under this Constitution constitutes a quorum. (3) Any reference in this Constitution to the votes of— (a) half of the membership of a body whose membership is not a multiple of two; (b) two-thirds of the membership of a body whose membership is not a multiple of three; or (c) three-quarters of the membership of a body whose membership is not a multiple of four;