Let . Then, the number of relations containing and which are reflexive and symmetric but not transitive, is
Let . Then, the number of relations containing and which are reflexive and symmetric but not transitive, is
Solution
We are given and the relation must contain and .
Since the relation is reflexive, for every .
So must contain .
Since the relation is symmetric, whenever , then .
So the minimum relation is:
The only remaining symmetric pair that can optionally be included is and .
This gives two candidate relations:
Checking for transitivity:
and , so we need .
But , so transitivity fails.
is not transitive. ✓
Checking for transitivity:
contains all 9 pairs in , making it the universal relation.
For any and in , is always in .
is transitive. ✗
Only satisfies all conditions: reflexive, symmetric, contains and , but not transitive.
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