  We investigate the growth of a crystal that is built by depositing cubes onto
the inside of a corner. The interface of this crystal evolves into a limiting
shape in the long-time limit. Building on known results for the corresponding
two-dimensional system and accounting for the symmetries of the
three-dimensional problem, we conjecture a governing equation for the evolution
of the interface profile. We solve this equation analytically and find
excellent agreement with simulations of the growth process. We also present a
generalization to arbitrary spatial dimension.
