Neither fraud nor concealment is present here. The cases of Berger v. Burkoff, 200 Md. 561, 92 A.2d 376 ( Ct. App. 1952); Allen v. Reichert, 73 Ariz. 91, 237 P.2d 818 ( Sup. Ct. 1951); Combow v. Kansas City Ground Investment Co., 358 Mo. 934, 218 S.W.2d 539, 8 A.L.R.2d 213 ( Sup. Ct. 1949); Otto v. Bolton Norris, 2 K.B. 46, 1 All Eng. 960 (1936); and the cases collected in 8 A.L.R.2d 218 (1949), support defendant's contention. The authorities cited by plaintiffs to avoid the established doctrine fall into two groups.