  We report results for the angular three-point galaxy correlation function in
the APM survey and compare them with theoretical expectations. For the first
time, these measurements extend to sufficiently large scales to probe the
weakly non-linear regime. On large scales, the results are in good agreement
with the predictions of non-linear cosmological perturbation theory, for a
model with initially Gaussian fluctuations and linear power spectrum $P(k)$
consistent with that inferred from the APM survey. These results reinforce the
conclusion that large-scale structure is driven by non-linear gravitational
instability and that APM galaxies are relatively unbiased tracers of the mass
on large scales; they also provide stringent constraints upon models with
non-Gaussian initial conditions and strongly exclude the standard cold dark
matter model.
