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## Main Question or Discussion Point

I freely admit that I am notationally challenged, so please help me out with this:

(from Enderton, A Mathematical Introduction to Logic)

[tex]\{x,y\} = \{y,x\}[/tex]

how does [itex]<x,y> = \{\{x\},\{x,y\}\} [/itex] define the

(from Enderton, A Mathematical Introduction to Logic)

I'm baffled. SinceThe ordered pair <x,y> of objects x and y must be defined in such a way that

[tex]<x,y>=<u,v> \mbox{ iff } x=u \qquad \mbox{ and } \qquad y=v[/tex]

Any definition that has this property will do; the standard one is

[tex]<x,y> = \{\{x\},\{x,y\}\}.[/tex]

[tex]\{x,y\} = \{y,x\}[/tex]

how does [itex]<x,y> = \{\{x\},\{x,y\}\} [/itex] define the

**ordered**pair [itex]<x,y>[/itex]?
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