Fear of trains fear about rail travel was heightened after British surgeon John Eric Erichsen described a post-traumatic diagnosis known as railway spine or "Erichsen's disease". People diagnosed with this had no obvious injury and were rejected as fake. Nowadays it is known that traffic accidents may cause posttraumatic stress disorder. It has been variously called as "train phobia", "railroad phobia", "dread of railway travel", etc. The German term "Eisenbahnangst" used, e.g., by Sigmund Freud was literally converted into Greek as "siderodromophobia" (Eisen = sideron = iron, Bahn = dromos = way, Angst = phobos = fear). In cases when this anxiety exceeds
Irrational number then no integral power of it can be an integer, as in lowest terms there must be a prime in the denominator that does not divide into the numerator whatever power each is raised to. Therefore, if an integer is not an exact "k" power of another integer, then that first integer's "k" root is irrational. Perhaps the numbers most easy to prove irrational are certain logarithms. Here is a proof by contradiction that log 3 is irrational. Notice that log 3 ≈ 1.58 > 0. Assume log 3 is rational. For some positive integers "m" and "n", we have