Non-PRO English Art/Literary Other

The threat of being turned into a comedy of itself. and even the temptation of turning itself into a comedy by itself, are real possibilities of theory, ones that are not accidental either. They too derive from theory's constitutive relation to the theater and is [sic! - KH] testimony to the fact that even the end of theory is still played out in the theater.


How should I understand "is" in the place marked with [sic!]?