Write SQL query to solve given problem: How many authors does the paper "Equation Solving in Geometrical Theories" have?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT COUNT(T1.AuthorId) FROM PaperAuthor AS T1 INNER JOIN Paper AS T2 ON T1.PaperId = T2.Id WHERE T2.Title = 'Equation Solving in Geometrical Theories'