In computational complexity theory, the complexity class ELEMENTARY of elementary recursive functions is the union of the classes E L E M E N T A R Y = ⋃ k ∈ N k - E X P = D T I M E ∪ D T I M E ∪ D T I M E ∪ ⋯ {\displaystyle {\begin{aligned}{\mathsf {ELEMENTARY}}&=\bigcup _{k\in \mathbb {N} }k{\mathsf {{\mbox{-}}EXP}}\\&={\mathsf {DTIME}}\left\cup {\mathsf {DTIME}}\left\cup {\mathsf {DTIME}}\left\cup \cdots \end{aligned}}} The name was coined by László Kalmár, in the context of recursive functions and undecidability; most problems in it are far from elementary. Wikipedia