What Is the Face Transition?

The simplest face transition every one of us has experienced, for example, is when e ice melts into water. This is so called the first order face transition and er. So this is what we mean by face transition. Of course, if a face transion could be way more complicated, they'd no't have to be first order a theye, can be any order. It depends on the no mathematical how some mathematical quantities behave. But generally we divide them into first order and the higher order. And the higher order we con second order face transitions. There can be a point where essential phases coexist - but in reality it's hard to realize.