The point is, people who deny the holocaust are liars, not real historians.

The fact that enormous numbers of people were systematically murdered as a deliberate act of policy by the Nazi regime, and that Jews were a particular target selected in this process - that is not open to genuine question. And that is where Holocaust Denial fits in.

But real historians do have to be open to the process of revising existing understandings of history to take account of information that was not previously available or was not taken into account. "Revisionism" is a reasonable label for this process.

This means that holocaust deniers have a motive to try to disguise their lies as "revisionism", and they do this.

This kind of thing has an effect of blurring the distinction between genuine historians who are honestly re-examining historical data and people such as holocaust deniers who have completely different motivations. "Revisionism" gets used as a dirty word for a dirty enterprise.

However there is still a place for investigating the Holocaust - how it came about, what exactly happened, what were its consequences, and how has the narrative that emerged about it affected subsequent events. And all these are topics where a kind of "revisionism" can be appropriate - and it would be wrong to use that term as a way of excluding this kind of investigation.

The same kinds of issues arise in relation to other historic crimes and disasters, which have rightly taken on a major role in the way descendants of survivors have interpreted the world and have acted, such as the Slave Trade or the Irish Famine.

Basically, there is a revisionism that seeks to reveal the truth, and a revisionism that seeks to conceal the truth - and the distinction between these two matters.