[throwawaymaths]

I think it's still considered a ponzi scheme if you tell people exactly what you are doing.

[epgui]

I believe that may be correct, although in practice there is often/usually/historically-always (?) deception involved, because presumably no morally competent adult would willingly give their money to an honest Ponzi unless they knew they stood to benefit by being one of the first to pull out.

But as you point out, I don't think deception per se is really the defining feature of the Ponzi.