Old Possum's Book of Practical Cats is a book of poems about cats. The cats in these poems act like humans. It is by T. S. Eliot. It was first sold in 1939. Andrew Lloyd Webber used most of the poems in his musical "Cats".
Contents of "Old Possum's Book of Practical Cats" by T. S. Eliot:
Concatenation
Concatenation is a simple concept from computer science. It is a way of making a new word (or String), by putting together two other Strings. Given the words "foo" and "bar", the two new words "foobar" and "barfoo" can be made that way.
Identity element
In mathematics, the identity element (or neutral element) of a set is a special element of that set. It is special because if it is combined with another element of that set, it does not change the other element.
With addition, the identity element is 0, because adding 0 to some number does not change the number. With multiplication, it is 1. In a group (an algebraic structure in mathematics), the identity element is sometimes denoted by the symbol formula_1.
Inverse function
An inverse function is a concept of mathematics. A function will calculate some output formula_1, given some input formula_2. This is usually written formula_3. The inverse function does the reverse. Let's say formula_4 is the inverse function of formula_5, then formula_6. Or otherwise put, formula_7. An inverse function to formula_5 is usually called formula_9. It is not to be confused with formula_10, which is a reciprocal function.
If formula_11 over real formula_2, then formula_13
To find the inverse function, swap the roles of formula_2 and formula_1 and solve for formula_1. For example, formula_17 would turn to formula_18, and then formula_19. This shows that the inverse function of formula_17 is formula_21.
Not all functions have inverse functions: for example, function formula_22 has none (because formula_23, and formula_24 cannot be both 1 and -1), but every binary relation has its own inverse relation.
In some cases, finding the inverse of a function can be very difficult to do.
Countable set
In mathematics (particularly set theory), a countable set is a set whose elements can be counted. A set with one thing in it is countable, and so is a set with one hundred things in it. A set with all the natural numbers (counting numbers) in it is countable too. This is because even if it is infinite, someone who counts forever would not miss any of the numbers. The sets which has the same size as the natural numbers are therefore called countably infinite. The size of these sets are then written as formula_1(aleph-null)—the first of the aleph numbers. Sometimes when people say 'countable set' they mean countable and infinite. Georg Cantor coined the term.
Countable sets include all sets with a finite number of members, no matter how many.
Countable sets also include some infinite sets, such as the natural numbers. Since it is impossible to actually count infinite sets, we consider them countable if we can find a way to list them all without missing any. The natural numbers have been nicknamed "the counting numbers", since they are what we usually use to count things with.
You can count the natural numbers with formula_2
You can count the whole numbers with formula_3
You can count the integers with formula_4
You can count the square integer numbers with formula_5
The rational numbers are also countable, but its counting becomes tricky. We can't just list the fractions as (0/1, 1/1, -1/1, 2/1, -2/1...) since we will never get to 1/2 this way. However, we can list all of the rational numbers in the form of a table. The horizontal rows are the numerators, while the vertical columns are the denominators. We can then zigzag through the list, starting at 1/1, then 2/1, then 1/2, then 1/3, then 2/2, then 3/1, then 4/1, then 3/2, then 2/3, etc. If we keep this up, we will get to all of the numbers on the table in due time. Each time we hit a new rational number that is new, we add it to the list of counted numbers. We don't want to count numbers twice, so when we hit 3/6, for example, we can skip it, because we already counted the rational number 1/2. In this way, we produce an infinite list with all the rational numbers. Therefore, the rational numbers are countable.
Suppose the integers are counted differently, as
This does not prove that the integers are uncountable, but it does illustrate what one might call a "failed" effort to count a set, because it is never possible to reach formula_7. Not all sets are countable. For example, the interval formula_8 and the set of real numbers can be proven to be uncountable.
Computable function
A computable function is an idea from computer science. A function is computable if there is an algorithm that can work out its result in a finite number of steps.
Computability theory is all about such functions.
Pharmacist
A pharmacist is a person who works in a pharmacy. Pharmacists have to be trained to work there, and have knowledge about the drugs package. Pharmacists interact with customers, give the prescribed medication and telling them about the drugs.
Thoosa
In Greek mythology, Thoosa was the name of the mother of the cyclops Polyphemus.
Perch
Perch is a type of fish. Perch are the fish in the genus "Perca".
Perch have "rough" scales. When looking through a microscope, the scales look like a plate with growth rings and spikes on the top edges. On the top side of the fish, there is a mouth, a pair of nostrils, and two lidless eyes. On the bottom sides are the "operculum", which are used to protect the gills. Also perch have a lateral line system, which a set of sense organs that are sensitive to vibrations in the water. They have a pair of pectoral and pelvic fins. On the front end of the fish, there are two dorsal fins. The first one is spiny and the second is soft. There is also an anal fin, which is also considered spiny, and a caudal fin.
Puce
Puce is a medium grayish red-violet colour.
"Puce" colours may be pale grayish red-violet, grayish red or brownish-purple colours.
Basically, puce colours are reddish purple colours mixed with gray or brown. A wide range of tones of puce are shown below.
Chinese dried plums, a favorite snack among Chinese people worldwide, can be said to be puce coloured.
The name is from the French word "puce" which means "flea". Some people say that the colour name comes from the colour of a squashed flea or the colour of a flea full of blood. Other people say that colour name comes from the flea's droppings of digested blood, which spread out in deep red stain when water contacts them. Still others say that the colour name means the colour of the belly of a flea.
On the other hand, the colour name may refer to blue-lavender of the Pennyroyal flower, also named "puce" in French. The name may come from the use of strong-smelling Pennyroyal to ward off fleas.
The Oxford English Dictionary (OED) dates the use of "puce" (in "couleur puce")in English from 1787. The first recorded use of "puce" as a color name was in the 14th century, in the French language.
Scarlet
Scarlet is a slight brilliant red colour. It is a colour of the rainbow. It is redder than vermilion. The colour's name comes from the Persian "saqirlat".
An early recorded use of "scarlet" as a color name in the English language dates to 1250.
League
The word league can mean one of the following:
Worship
Worship is a word often used in religion. It means to have much respect. If someone prays or says thank to God, people say that they are worshipping God. Worship can also be used as the name for a church service or similar event. This can be called an act of worship.
The Quran talks about worshipping Allah.
Claudius