infix :

Create a Sequence that is stepping through this interval skipping values. For a
non-negative step parameter, the stream will return lower, lower+step,
lower+2*step, etc. as long as these values are <= upper.

For a negative step parameter, the stream will return upper, upper+step,
upper+2*step, etc. as long as these values are >= lower. Note that this means
that a negative step will produce a non-empty stream for an empty interval with
lower > upper!