I need to write a long list of numbered equations. I know that I could use the environments gather or align, but either with the gather environment I cannot have any alignment or with the align environment I should have a point of alignment which is good for all my equations, which is not the case.
For example, let us say that I have four equations, and I would like to align the equal signs of equations (1) and (2) and the two equal signs of equations (3) and (4). But I do not want to align the equal signs of equation (2) and (3). Now if I write two align environments with two equations each, the vertical space between equation (2) and equation (3) is bigger than the vertical space between equations (1)-(2) and (3)-(4). How can I avoid this and get coherent vertical spacing? Or alternatively, is there a more clever way to align a long list of equations with different aligning points?