  The main purpose of this short note is to present an adaptation of the
multilinear Bellman function technique from [4] to the time-frequency analysis.
Demeter and Thiele introduced the two-dimensional bilinear Hilbert transform in
[3] and showed that the Carleson operator can be identified in particular
instances of the corresponding trilinear form. Demeter considered the Walsh
model of one such form in [2], in relation to the discussion of the
Walsh-Carleson theorem. We prove boundedness of this trilinear form for a
single triple of exponents at the boundary of the previously established range.
