Hmm. Seen flat and tried it. in Arc2 flat works recursively, turning (list (list 1 2) (list (1 2)) into (1 2 1 2), which doesn't produce the desired (2 4) when combined with map +
The apply function takes a function, any number of arguments, and a list, to wit (apply f x0 x1 x2 ... xN args). This is the same as (f x0 x1 x2 ... xN args.0 args.1 args.2 ... args.M). This allows you to construct argument lists at runtime, which can come in very handy.
