Archangel Macsika
Prove or disprove that if R and S are antisymmetric, then so is: (a) (R ∪ S) (b) (R ∩ S)
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a)
If R and S are antisymmetric, then R ∪ S is antisymmetric. We disprove the statement.
(1) Let T = {a, b}, R = {(a, b)}, and S = {(b, a)}.
(2). R and S are antisymmetric.
(3). R ∪ S = {(a, b),(b, a)}.
(4). ∃a, b,(a, b) ∈ R ∪ S ∧ (b, a) ∈ R ∪ S ∧ a 6= b. (Step 3)
(5). R ∪ S is not antisymmetric.
b)
(R ∩ S) is antisymmetric
Let S contains element which is symmetric to some element in R. But this element will not be included in (R ∩ S) because S does not contain this element. So, R remains antsymmetric.
The same is for S.