 Some authors write ‘\(\lambda x.M\)’ or ‘\(\lambda x\cdot M\)’, with a full stop or a centered dot separating the bound variable from the body of the abstraction term. As with the square brackets, these devices are intended to assist reading \(\lambda\)-terms; they are usually not part of the official syntax. (One sees this device used in earlier works of logic, such as Principia Mathematica, where the function of the symbol . in expressions such as ‘\(\forall x\).\(\phi\)’ is to get us to read the whole of the formula \(\phi\) as under the scope of the \(\forall x\).)