# Differences

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+ | =====Directed graphs===== | ||

+ | |||

+ | Abbreviation: **DiGraph** | ||

+ | |||

+ | ====Definition==== | ||

+ | A \emph{directed graph} (or \emph{digraph} for short) is a structure $\mathbf{G}=\langle G,E\rangle$ such that | ||

+ | |||

+ | $E$ is binary relation on $G$: $E\subseteq G\times G$ | ||

+ | |||

+ | Remark: This is a template. | ||

+ | If you know something about this class, click on the 'Edit text of this page' link at the bottom and fill out this page. | ||

+ | |||

+ | 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 $\mathbf{G}$ and $\mathbf{H}$ be directed graphs. A morphism from $\mathbf{G}$ to $\mathbf{H}$ is a function $h:G\rightarrow H$ that preserves $E$: | ||

+ | $\langle x,y\rangle\in E^{\mathbf G}\Longrightarrow \langle h(x), h(y)\rangle\in E^{\mathbf H}$ | ||

+ | |||

+ | ====Definition==== | ||

+ | An \emph{...} is a structure $\mathbf{A}=\langle A,...\rangle$ of type $\langle | ||

+ | ...\rangle$ such that | ||

+ | |||

+ | $...$ is ...: $axiom$ | ||

+ | |||

+ | $...$ is ...: $axiom$ | ||

+ | |||

+ | ====Examples==== | ||

+ | Example 1: | ||

+ | |||

+ | ====Basic results==== | ||

+ | |||

+ | |||

+ | ====Properties==== | ||

+ | Feel free to add or delete properties from this list. The list below may contain properties that are not relevant to the class that is being described. | ||

+ | |||

+ | ^[[Classtype]] |variety | | ||

+ | ^[[Equational theory]] |decidable | | ||

+ | ^[[Quasiequational theory]] |decidable | | ||

+ | ^[[First-order theory]] |undecidable | | ||

+ | ^[[Locally finite]] | | | ||

+ | ^[[Residual size]] | | | ||

+ | ^[[Congruence distributive]] |no | | ||

+ | ^[[Congruence modular]] |no | | ||

+ | ^[[Congruence $n$-permutable]] |no | | ||

+ | ^[[Congruence regular]] |no | | ||

+ | ^[[Congruence uniform]] |no | | ||

+ | ^[[Congruence extension property]] | | | ||

+ | ^[[Definable principal congruences]] | | | ||

+ | ^[[Equationally def. pr. cong.]] | | | ||

+ | ^[[Amalgamation property]] |yes | | ||

+ | ^[[Strong amalgamation property]] |yes | | ||

+ | ^[[Epimorphisms are surjective]] | | | ||

+ | |||

+ | ====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==== | ||

+ | |||

+ | [(Ln19xx> | ||

+ | F. Lastname, \emph{Title}, Journal, \textbf{1}, 23--45 [[MRreview]] | ||

+ | )] | ||

+ | |||

+ | |||

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