"and you shall stone them with stones": I might think, with many stones; it is, therefore, written (Vayikra 20:2) "with a stone." I might then think, with one stone. It is, therefore, written "with stones." How is this to be resolved? If he is not killed with the first stone, he is killed with the second.
(Devarim 17:6) "By word of two witnesses or three witnesses is the dead one to be put to death": This tells me only of those who are put to death in this context. Whence do I derive (the same for) the others who are put to death (by beth-din)? From "By word of two witnesses or three witnesses is the dead one to be put to death."