I'm pretty sure FLS is banging his head against the wall right now.
Maybe not in FAA terms, but in strict engineering terms,
V(stall) = (2W/(rho*S*CL(max)))^.5
So, I don't see why you guys keep talking stall when he clearly says "stall speed".
He stipulated: CLMax (alpha crit) and level flight (neither descending nor ascending, thus in equilibrium, L=mg).
If that condition obtains, any decrease in speed (lift = 5 rho v^2 cl S, mg = constant for our purpose here, albeit time-dependent in reality) will result in a lift decrease and you will descend, any increase and you will ascend.
Okay, so he might be mis-quoting the book - but his statement is entirely logical and correct.
Traveler is also correct in stating "there is no speed at which a stall can't happen", but that is a fundamentally different statement than that made by the equation I cite (eg, accelerated stall is entirely possible above the stall speed). Oldman's statement is also correct - but misses the point of the definition, though, I'll note, the equation in no way cares that you be in level flight but rather only cares that you are in vertical force equilibrium.
You guys need a referee and a translator.