define seq(a, b) a

strategy basic-difference
  minimum-change = 5.0e-4 <- slider(1.0e-4, 1.0e-3, 5.0e-5),
  scale = 200 <- slider(1, 500)
  last-value = 0
  history ->
    let new-value = history[0],
        last-value = seq(last-value, last-value <- new-value),
        delta = abs(new-value - last-value) in
      if delta > minimum-change then
        if last-value > new-value
        then sell(scale * delta)
        else buy(scale * delta)