Fear of flying persistent fear or anxiety when they consider flying, as well as during flying. They will avoid flying if they can, and the fear, anxiety, and avoidance cause significant distress and impair their ability to function. Take-off, bad weather, and turbulence appear to be the most anxiety provoking aspects of flying. The most extreme manifestations can include panic attacks or vomiting at the mere sight or mention of an aircraft or air travel. Around 60% of people with fear of flying report having some other anxiety disorder. The causes of flight phobia and the mechanisms by which it is maintained were
Irrational number formula_31. It is not known if formula_32 Catalan's constant, or the Euler–Mascheroni constant formula_33 are irrational. It is not known if either of the tetrations formula_34 or formula_35 is rational for some integer formula_36 Since the reals form an uncountable set, of which the rationals are a countable subset, the complementary set of irrationals is uncountable. Under the usual (Euclidean) distance function d("x", "y") = |"x" − "y"|, the real numbers are a metric space and hence also a topological space. Restricting the Euclidean distance function gives the irrationals the structure of a metric space. Since the subspace of irrationals