When I was at university four decades ago, debate raged about the evils of racism, capitalism, colonialism, orientalism and of course, the biggies, sexism.  The problem with the various isms was that they contradicted each other.  Thus if blacks were oppressed by whites, did that mean that white women oppressed black men — and if all homosexuals and lesbians were oppressed by straight people then were black straight men and white straight women jointly participating in the oppression of black lesbians?

It is a problem which has bubbled away for half a century and, until now, there was really no answer...