  Numerical integrations of the closely-packed inner Uranian satellite system
show that variations in semi-major axes can take place simultaneously between
three or four consecutive satellites. We find that the three-body Laplace angle
values are distributed unevenly and have histograms showing structure, if the
angle is associated with a resonant chain, with both pairs of bodies near
first-order two-body resonances. Estimated three-body resonance libration
frequencies can be only an order of magnitude lower than those of first-order
resonances. Their strength arises from a small divisor from the distance to the
first-order resonances and insensitivity to eccentricity, which make up for
their dependence on moon mass. Three-body resonances associated with
low-integer Laplace angles can also be comparatively strong due to the many
multiples of the angle contributed from Fourier components of the interaction
terms. We attribute small coupled variations in semi-major axis, seen
throughout the simulation, to ubiquitous and weak three-body resonant
couplings. We show that a system with two pairs of bodies in first-order
mean-motion resonance can be transformed to resemble the well-studied
periodically-forced pendulum with the frequency of a Laplace angle serving as a
perturbation frequency. We identify trios of bodies and overlapping pairs of
two-body resonances in each trio that have particularly short estimated
Lyapunov timescales.
