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Quasitrivial groupoids

Abbreviation: QtGrpd

Definition

A \emph{quasitrivial groupoid} is a groupoid A=A, such that

is \emph{quasitrivial}: xy=x or xy=y

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It is not unusual to give several (equivalent) definitions. Ideally, one of the definitions would give an irredundant axiomatization that does not refer to other classes.

Morphisms

Let A and B be quasitrivial groupoids. A morphism from A to B is a function h:AB that is a homomorphism: h(xy)=h(x)h(y)

Definition

An \emph{…} is a structure A=A, of type such that

is …: axiom

is …: axiom

Examples

Example 1:

Basic results

Quasitrivial groupoids are in 1-1 correspondence with reflexive relations. E.g. a translations is given by xy=x iff x,yE.

Properties

Finite members

$\begin{array}{lr}

f(1)= &1\\
f(2)= &\\
f(3)= &\\
f(4)= &\\
f(5)= &\\

\end{array}\begin{array}{lr}

f(6)= &\\
f(7)= &\\
f(8)= &\\
f(9)= &\\
f(10)= &\\

\end{array}$

Subclasses

[[...]] subvariety
[[...]] expansion

Superclasses

[[...]] supervariety
[[...]] subreduct

References


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