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A detailed tutorial on how to determine Dedekind cuts. Step by step tutorial including several examples of Dedekind cuts for reference.

A Dedekind cut is a partition of rational numbers into two non-empty sets A and B, such that all elements of A are less than elements of B, and A has no greatest element. The cut itself is a gap that is located between A and B, which is normally found by creating a new, irrational number, and setting it in the gap. What irrational number you use depends on what numbers you have partitioned into the two sets. It is like the number line of advanced algebra, that has both rational and irrational numbers on it instead of just integers. The Dedekind cut was named after Richard Dedekind.

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A detailed tutorial on how to construct a Cayley table. Step by step tutorial including several examples of how to construct a Cayley table for reference.

A Cayley table is a table that expresses the structure of a finite set. A Cayley table is set up by having the elements of the set across the first row, and numbers going in a numerical order of n + 1 starting at 1 down the first column. Sometimes the table is simply different ways the elements can be ordered. Other times is is a true table, where an operation is performed between two numbers in the space where they cross each other. However, a true Cayley table must be constructed using an identity skeleton. Once an identity skeleton for the finite set has been decided on, the Cayley table can be filled out using the identity skeleton. Since there is more than one possible identity skeleton for a finite set, you may have to go through a trial and error process until you find the right one.

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A detailed tutorial on the definition of cardinal numbers. Step by step tutorial including several examples of how to define cardinal numbers for reference.

Cardinal numbers are natural numbers that are used to measure cardinality of sets. Cardinality is a fancy way of saying the size of a set. This means the cardinality is the number of elements in a set, provided that the set is finite. If the set is infinite, something called a transfinite cardinal number is used to describe the cardinality of the set. Cardinal numbers are a very important part of set theory, even though they are not studied often or used constantly.

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A detailed tutorial on the pigeon-hole principle. Step by step tutorial including several examples of the pigeon-hole principle for reference.

The pigeon-hole principle is an important principle in math that states that if n items are to be put into m pigeon-holes, and n > m, then at least one pigeon-hole must contain more than one item. It is thought of as an extension of the counting principle. The pigeon-hole principle was first referred to as the drawer principle, or the shelf principle. Because of this, it is commonly called Dirichlet’s box principle or Dirichlet’s drawer principle. It is most commonly used with finite sets of elements; however, this principle can also be used with infinite sets.

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A detailed tutorial on the definition of an outlier. Step by step tutorial including several examples of definitions of outliers for reference.

An outlier is a type of observation of statistical data. It is usually very far away from the other values in the data set, hence the name. Usually it is a number that is much smaller than the other numbers, although it could be much larger than the other numbers as well. Outliers have an equal chance of occuring in any random observation, but they are still rare. Typically when an outlier is found it means there is some sort of mistake, usually a measurement error.

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A detailed tutorial on families of sets. Step by step tutorial including several examples of families or collections of sets for reference.

Families of sets are closely linked with indexed sets – the only sets that can be indexed are families of sets. A family of sets is basically a set of sets. An example would be a power set (the set of all subsets of a set). Unions and intersections can also be performed with families of sets. Instead of concerning just two sets, they concern every single set in the family of sets. The union and intersection over a family of sets are known as extended set operations.

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A detailed tutorial on complements in set theory. Step by step tutorial including several examples of complements in set theory for reference.

In set theory, a complement is the opposite of something. It works a little like negation, in that the complement of a set is everything but that set. The way to find this is to subtract the set from its universe, which is a larger set that the set you are taking a complement of belongs to. You can think of your set as a subset of the universe.

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A detailed tutorial of the notation in set theory. Step by step tutorial including several examples of the notation in set theory for reference.

The notation for set theory, also called set notation or set-builder notation, is simple. It consists of a special curled bracket enclosing the elements of the set. It also includes a variable, x. When using the notation for set theory, your elements will be arranged such as {x|x = …}. You could have what x is equal to, what x in not equal to, you could say that x is less than or greater than something, or that x must be something. Whatever x is, is part of your set. If x is a natural number less than 2, then your only element is 1. Reading the set and writing the set is not difficult, but can be confusing if you don’t understand that all x stands for is all the elements of the set, and has no significance outside of that.

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A detailed tutorial on the definition of a finite set. Step by step tutorial including several examples of finite sets for reference.

There are many different types of sets, but one of the most common ones to run into a finite sets. A finite set is a set that has a finite number of elements – meaning a set with a definite number of elements, such as five, or ten. The number of elements in the set must be a natural number, and it is called the cardinality of a set. An empty set is considered to be finite, with a cardiality of zero, even though zero is not considered to be a natural number.

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A detailed tutorial on disjoint sets. Step by step tutorial including several examples of disjoint sets and how to identify disjoint sets for reference.

A disjoint set is a term applied in set theory when two or more sets have no elements in common. For example, the sets {1, 2, 3} and {7, 8, 9} are disjoint sets because none of the numbers in the sets are the same. The formal way to say this is that two sets are disjoint sets if their intersection creates an empty set, in other words, nothing at all. An intersection is when you only take the values that are found in both sets. If none of the values are the same, this would be an empty set. Disjoint sets can be classified into further categories of piecewise, pairwise, or mutually disjoint provided that in a collection, at least two sets are disjoint.