Can a Positive Charge be in Stable Equilibrium in the Center of a Square According to Earnshaw's Theorem?

[lamp post]

we have got four charges placed at the ends of a square. if we palce a positive charge in the center, it appeares to be in stable equillibrium; yet earnshaw's theorem(that no particle can be in stable equillibrium if it is under the action of electrostatic forces only) holds. Why is that?

 

[Chandra Prayaga]

Earnshaw's theorem

The charge at the center of the square is in equilibrium, yes. But it is not in stable equilibrium. Stable equilibrium means that if you move the charge slightly in any direction, then it should return to the center. In this case, as in every other case involving electrostatic forces only, if you move the charge, from the center, it will not return. Check that out.