In the early 20th century, Bertrand Russell gave a different complete axiomatization of propositional logic, considered on its own, in his 1906 paper "The Theory of Implication", and later, along with A. N. Whitehead, produced another axiomatization using disjunction and negation as primitives in the 1910 work Principia Mathematica . Proof of the possibility of defining all truth functional operators in virtue of a single binary operator was first published by American logician H. M. Sheffer in 1913, though American logician C. S. Peirce (1839-1914) seems have discovered this decades earlier. In 1917, French logician Jean Nicod discovered that it was possible to axiomatize propositional logic using the Sheffer stroke and only a single axiom schema and single inference rule.
The pitch trimmer is a small handle not unlike a window-winder, set on the left-hand cockpit wall. It is low-geared, taking five turns from full aft to full nose-down trim. No position indicator is provided other than a light, one of an array of six on the panel, which indicates neutral trim. Once out of neutral the light is extinguished. If the light is out when commencing the starting procedure, you have to wind the handle to establish the neutral datum before setting the desired trim. Other annunciation lights in the same block show Fuel low, Gen. fail, while further along the panel is a set of just two red lights. These augment the stall warner by flashing Slow and Stall as the aircraft approaches the stalling speed.
Much of the variation in tasting of PTC is associated with polymorphism at the TAS2R38 taste receptor gene.  In humans, there are three SNPs ( single nucleotide polymorphisms ) along the gene that may render its proteins unresponsive.  There is conflicting evidence as to whether the inheritance of this trait is dominant or incompletely dominant .  Any person with a single functional copy of this gene can make the protein and is sensitive to PTC. [ citation needed ] Some studies have shown that homozygous tasters experience a more intense bitterness than people that are heterozygous ; other studies have indicated that another gene may determine taste sensitivity.