  This is an appendix to the recent paper of Favacchio and Guardo. In these
notes we describe explicitly a minimal bigraded free resolution and the
bigraded Hilbert function of a set of 3 fat points whose support is an almost
complete intersection (ACI) in $\mathbb{P}^1\times\mathbb{P}^1.$ This solve the
interpolation problem for three points with an ACI support.
