In another notation, δ W is written đ W (with a horizontal line through the d). This notation indicates that đ W is not an exact one-form. The line-through is merely a flag to warn us there is actually no function (0-form) W which is the potential of đ W. If there were, indeed, this function W, we should be able to just use Stokes Theorem to evaluate this putative function, the potential of đ W, at the boundary of the path, that is, the initial and final points, and therefore the work would be a state function. This impossibility is consistent with the fact that it does not make sense to refer to the work on a point in the PV diagram; work presupposes a path.