step
Creates a progression with the same direction and a new positive step magnitude.
The magnitude replaces the current step; it is not multiplied by it. The final element is aligned again using first and last. Empty progressions stay empty.
Receiver
the progression whose bounds and direction are retained.
Return
a new progression with the original direction and requested magnitude.
Parameters
step
the positive magnitude of the new step.
Throws
if step is not positive.