well here is an attempt at translating the equation to expr, but it's broken...
i suspect my algebra is not up to scratch or the equation isnt right. either way the process should at least demonstrate how to translate equations into expr.
i didnt try the second equation... also it may be useful to explain the context of the equations, as this might make it easier for others to help.
hope that's vaguely useful, sorry dont have much time to look into this.
think [bucket 2 1] might be better, cos it outputs current value and previous value. otherwise it outputs previous and one before previous (ignores current value)... look at float number boxes and it should explain better!