“…The only exception is that we denote the field strength by F in order not to mix it up with Minkowksi's F . For other presentations of Maxwell's equations in exterior calculus, see, e.g., Bamberg & Sternberg [5], , Delphenich [8,9], Frankel [14], Jancewicz [27], Lindell [34], Misner, Thorne & Wheeler [41], Russer [51], Thirring [60], and Trautman [61]. 3 We call a structure premetric, if it can be defined "before" a metric is available (or a metric exists, but it is not used).…”