For the purposes of this chapter –

(a) every act of conspiring with any person to effect any intention mentioned in this chapter;

(b) every act done in furtherance of such purpose by any of the persons so conspiring;

(c) the writing of any words expressive of such intention; and

(d) the speaking of any such words if accompanied by or explanatory of any act in furtherance of such intention –

shall be deemed to be an overt act manifesting such intention.