let A={0,1,2,3,∞}
here x=0, y=∞, a_{1}=1, a_{2}=2, a_{3}=3.
∞ ∞
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1 and 3
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2 1
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3 2
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0 0
is a Toset is also a Toset
bcz as mentiond in question , ≤ is applicable only for (x,a_{1}) and (a_{3},y), however a_{1}, a_{2}, a_{3 }(1,2,3) can be permutate in any order (3!=6) as long as x has leat value and y has greatest value in the set. same thing applicable for your query, i think.