A job I would not want to do
The us patent office must figure out who had the conception of an invention first. To quote the US patent law, Conception is the "formation in the mind of the inventor, of a definite and permanent idea of the complete and operative invention, as it is hereafter to be applied in practice." Hybritech Inc. v. Monoclonal Antibodies, Inc., 802 F.2d 1367, 1376 (Fed. Cir. 1986) (quoting 1 Robinson On Patents 532 (1890)). This is what must be determined to find out who is the original inventor if two or more people apply for a patent for the same invention. I don’t know how they do it but it seems to work for patents are issued and denied based on the investigation to make the determination.