Task: Text Categorization
Input (English): This letter represents a quantity defined as Gibbs free energy per surface area in the Young-Laplace equation. Relativistic mass equals rest mass times a quantity represented by this letter, which is equal to the derivative of time with respect to proper time. That quantity is also expressed as one divided by the square root of one minus v squared over c squared, known as the (*) Lorentz factor. In addition to symbolizing surface tension and photons, this letter names a type of high-energy decay and radiation carrying more energy than X-rays. For ten points, identify this third letter of the Greek alphabet.
Output (English): Science