  We show that the slow viscoelastic response of a foam is that of a power-law
fluid with a terminal relaxation. Investigations of the foam mechanics in creep
and recovery tests reveal that the power-law contribution is fully reversible,
indicative of a delayed elastic response. We demonstrate how this contribution
fully accounts for the non-Maxwellian features observed in all tests, probing
the linear mechanical response function. The associated power-law spectrum is
consistent with soft glassy rheology of systems with mechanical noise
temperatures just above the glass transition [Fielding et al., J.Rheol. 44,
323(2000)] and originates from a combination of superdiffusive bubble dynamics
and stress diffusion, as recently evidenced in simulations of coarsening foam
[Hwang et al., Nat.Mater. 15, 1031 (2016)].
