  We prove rigorously that the symmetric traceless and the antisymmetric tensor
models in rank three with tetrahedral interaction admit a $1/N$ expansion, and
that at leading order they are dominated by melon diagrams. This proves the
recent conjecture of I. Klebanov and G. Tarnopolsky in JHEP 10 (2017) 037
[arXiv:1706.00839], which they checked numerically up to 8th order in the
coupling constant.
