t, Sql Server - rextester

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CREATE TABLE A
    ([V1] int, [V2] int)
;
    
INSERT INTO A
    ([V1], [V2])
VALUES
    (1, 3),
    (1, 4),
    (3, 4),
    (1, 6),
    (6, 5)
;

SELECT *
FROM (
        SELECT source.[V1], source.[V2],
               target1.[V1] as t1_v1,
               target1.[V2] as t1_v2,
               target2.[V1] as t2_v1,
               target2.[V2] as t2_v2,
               CASE WHEN source.[V1] = target1.[V1] 
                    THEN target1.[V2]
                    ELSE target1.[V1]
               END as transitive1,
               CASE WHEN source.[V2] = target2.[V2] 
                    THEN target2.[V1]
                    ELSE target2.[V2]
               END as transitive2     
        FROM A as source
        JOIN A as target1
          ON      (source.[V1] = target1.[V1] OR source.[V1] = target1.[V2])
          AND NOT (source.[V1] = target1.[V1] AND source.[V2] = target1.[V2])
        JOIN A as target2    
          ON      (source.[V2] = target2.[V1] OR source.[V2] = target2.[V2])
          AND NOT (source.[V1] = target2.[V1] AND source.[V2] = target2.[V2])
     ) T
WHERE T.transitive1 = T.transitive2

View schema
Execution time: 0 sec, rows selected: 3, rows affected: 5, absolute service time: 0,16 sec