A proof that a discrete delta function is second-order accurate

It is proved that a discrete delta function introduced by Smereka [P. Smereka, The numerical approximation of a delta function with application to level set methods, J. Comput. Phys. 211 (2006) 77–90] gives a second-order accurate quadrature rule for surface integrals using values on a regular background grid. The delta function is found using a technique of Mayo [A. Mayo, The fast solution of Poisson’s and the biharmonic equations on irregular regions, SIAM J. Numer. Anal. 21 (1984) 285–299]. It can be expressed naturally using a level set function.