Profiles of density (star colored symbols) and velocity (black solid lines) as function of time at different heliospheric distances (from bottom to top: 0.1 AU, 0.3 AU, 0.5 AU, 0.55 AU, 0.6 AU, 0.8 AU and 1.0 AU) for the event of May 23, 2010. In the left panels we present these profiles with fixed axes to see the evolution of the interaction process while in the right panels a zoom to these figures was applied to clearly notice the structures involved, their interaction, and their evolution up to 1 AU. We tag each plasma in the density profiles with colored crosses: the solar wind before CME₁ in blue, the CME₁ in red, the solar wind between the CMEs in dark cyan, the CME₂ in amber and the solar wind after the CME₂ in green. While the interaction process takes place, it is observed the development of a third density peak between both ICMEs (clearly observed at 0.55 AU). This peak appears and disappears while the process occurs. Once it disappears completely, the merged region is formed (this time is similar with those obtained analytically and reported by Lugaz et al., 2012).