In a binary alloy system exhibiting two condensed phases $($solid and liquid$),$ if both the phases show positive departure from ideal behaviour, write down the conditions necessary for a syntectic invariant reaction to arise, as a result of interaction$/$intersection of phase boundaries. What are the consequences on the phase diagram if one or more of these conditions are violated. Also identify the thermodynamic conditions in terms of excess Gibbs energies in each phase. Explain with the help of neat schematic diagrams.

$[6]$