Application of fractional derivative with exponential law to bi-fractional-order wave equation with frictional memory kernelB. Cuahutenango-Barro, M. A. Taneco-Hernández and J. F. Gómez-AguilarEur. Phys. J. Plus, 132 12 (2017) 515DOI: https://doi.org/10.1140/epjp/i2017-11796-9