what is an evil twin?
An evil twin is two links with the same name, each pointing to a different element, in two different versions of the same directory element. The reason they are evil is because they create the appearance of a directory containing the same file on two different branches, when in fact they contain two different files with the same name. If this situation isn’t detected, then one can very well end up with two change histories of something that everybody thought of being the same file, only to get a rude surprise at merge time. There is essentially no good way to merge the two change histories. Evil twins get created when two developers concurrently add the same file to source control without coordination, or if one developer copies files from another developer’s view and puts those files under source control. Copying files around should be discouraged, but the best way to avoid evil twins is to create a pre-mkelem trigger that will search through some or all versions of the directory cont
