PSPACE
In computational complexity theory, PSPACE is the set of all decision problems that can be solved by a Turing machine using a polynomial amount of space. == Formal definition == If we denote by S P A C E ( f ( n ) ) {\displaystyle {\mathsf {SPACE}}(f(n))} the set of all problems that can be solved by Turing machines using O ( f ( n ) ) {\displaystyle O(f(n))} space for some function f {\displaystyle f} of the input size n {\displaystyle n} , then we can define P S P A C E {\displaystyle {\mathsf {PSPACE}}} formally as P S P A C E = ⋃ k ∈ N S P A C E ( n k ) .