A simpler normal number construction for simple Luroth series

Champernowne famously proved that the number $0.(1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)\mathrm{.}\mathrm{.}\mathrm{.}$ formed by concatenating all the integers one after another is normal base 10. We give a generalization of Champernowne’s construction to various other digit systems, including generalized L"uroth series with a finite number of digits. For these systems, our construction simplifies a recent construction given by Madritsch and Mance. Along the way we give an estimation of the sum of multinomial coefficients above a tilted hyperplane in Pascal’s simplex, which may be of general interest.