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it seems to me that for discussions of RST, one should use only _binary_ relations: if our relation is called ~, for example, the usual "infix" notation x~y means that the ordered pair (x,y) is an element of the set of ordered pairs called ~ (recall that a relation, by definition,
_is_ a set of ordered pairs).

the definitions you've pointed at (using the world's most famous _equivalence_ relation) seem to depend on the infix notation.

how are we to speak of reflexivitiy, for example, if we consider a trinary relation? i don't get it.



I'm not sure I follow your objection. All of the relations in my list are intended to be taken as binary relations.

X has-a-class-with Y, where X and Y are students, means that (X,Y) is in the set of ordered pairs that includes all pairs of students that have a class together.

I don't think any of my relations are trinary. Perhaps I need to make some of the definitions more clear?


my fault entirely; sorry.
i careless took your lines

congruent (R, S, T)
complementary-to (S)

as refering to a trinary
and unary relation respectively
(didn't notice that you'd
*clearly stated* that you were
providing "answers"; in the
unlikely event that anybody
else is still so confused,
R, S, and T have their "obvious"
meanings (reflexive, ...).

like that old lady used to say,
"never mind ..." ...


Not-equal-to is symmetric, but it's not reflexive.


ah yes, thanks xerxes...the post now reflects the correction.

Mrs. Scarpa

Do you by any chance have the lesson plan you used to teach this lesson? I am a beginning teacher interview for a position and I have to teach this for my demo lesson. Any help would be much appreciated.

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