Proper complexity function
Encyclopedia
A proper complexity function is a function f mapping a natural number
Natural number
In mathematics, the natural numbers are the ordinary whole numbers used for counting and ordering . These purposes are related to the linguistic notions of cardinal and ordinal numbers, respectively...

 to a natural number such that:
  • f is nondecreasing;
  • there exists a k-string Turing machine
    Turing machine
    A Turing machine is a theoretical device that manipulates symbols on a strip of tape according to a table of rules. Despite its simplicity, a Turing machine can be adapted to simulate the logic of any computer algorithm, and is particularly useful in explaining the functions of a CPU inside a...

     M such that on any input of length n, M halts after O(n + f(n)) steps, uses O(f(n)) space, and outputs f(n) consecutive blanks.


If f and g are two proper complexity functions, then f + g, fg, and 2f, are also proper complexity functions.

Similar notions include honest function, space-constructible function, and time-constructible function.
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