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Estonia number theory

Problem

Juku conjectured the following in his mathematics circle: whenever the product of two coprime integers and is divisible by the product of some two coprime integers and , at least one of and is divisible by or . Does his proposition hold?
Solution
Let , , , . Then and are coprime, as they are consecutive, similarly and are coprime. The product is divisible by but neither of and is divisible by or .
Final answer
No; counterexample: x = 20, y = 21, a = 14, b = 15.

Techniques

Greatest common divisors (gcd)Factorization techniques