claim: Prague's historic center is on UNIDO's list of World Heritage Sites.
evidence: In computability theory , computational complexity theory and proof theory , a fast-growing hierarchy -LRB- also called an extended Grzegorczyk hierarchy -RRB- is an ordinal-indexed family of rapidly increasing functions fα  : N → N -LRB- where N is the set of natural numbers -LCB- 0 , 1 , ... -RCB- , and α ranges up to some large countable ordinal -RRB- .. computability theory. computability theory. computational complexity theory. computational complexity theory. proof theory. proof theory. Grzegorczyk hierarchy. Grzegorczyk hierarchy. natural numbers. natural numbers. computational complexity. Computational complexity theory. A primary example is the Wainer hierarchy , or Lob -- Wainer hierarchy , which is an extension to all α < ε0 .. Such hierarchies provide a natural way to classify computable functions according to rate-of-growth and computational complexity .. computational complexity. Computational complexity theory