Multiplying both sides of the equation by leads to an equivalent form for the problem. As a polynomial equation with integer variables, this is an example of a Diophantine equation. The Hasse principle for Diophantine equations asserts that an integer solution of a Diophantine equation should be formed by combining solutions obtained modulo each possible prime number. On the face of it this principle makes little sense for the Erdős–Straus conjecture, as the equation is easily solvable modulo any prime. Nevertheless, modular identities have proven a very important tool in the study of the conjecture.