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
Proof that π is irrational enough and that the sequence of all "g" converges to 0. But a sequence of numbers greater than or equal to |"y"| cannot converge to 0. Since "f"(/4) = cos(/2) = 0, it follows from claim 3 that /16 is irrational and therefore that is irrational. On the other hand, since another consequence of Claim 3 is that, if "x" ∈ Q \ {0}, then tan "x" is irrational. Laczkovich's proof is really about the hypergeometric function. In fact, "f"("x") = "F"(k; −"x") and Gauss found a continued fraction expansion of the hypergeometric function using its functional equation. This allowed