Is there a key or combo to edit a formula in Apple's Numbers without using the mouse?

Is there a key or combo to edit a formula in Apple's Numbers without using the mouse?

In Excel (and OpenOffice) I could use F2 to edit the existing formula. So far the only 'shortcut' I've found in Numbers involves clicking the mouse. Since I'm going from moving with the keyboard to editing with the keyboard, I'd rather make the transition with the keyboard. Are there undocumented or clever ways to trigger formula editing?