Equation xy = yx
In general, exponentiation fails to be commutative. However, the equation x y = y x {\displaystyle x^{y}=y^{x}} has an infinity of solutions, consisting of the line x = y {\displaystyle x=y} and a smooth curve intersecting the line at ( e , e ) {\displaystyle (e,e)} , where e {\displaystyle e} is Euler's number.