Bud Lockett was a 4 kyu in New Mexico who formulated Lockett's Law for extensions: "Always extend an even number of spaces. Then your opponent will not know where to invade."
-- Bill Spight ;-)
-- cliftut; Funny thing is, there's some truth to this.
-- Warfreak2: On the contrary, one should always extend an odd number of spaces. Even extensions leave two obvious invasion points!