In such cases, one refers to the system as a [[flow (mathematics)|flow]]. (cf. Section on [[#Conjugacy|conjugacy]] below.)
NegativeIf a function is bijective (and so possesses an inverse function), then negative iterates correspond to function inverses and their compositions. For example, {{math|''f''<sup> −1</sup>(''x'')}} is the normal inverse of {{mvar|f}}, while {{math|''f''<sup> −2</sup>(''x'')}} is the inverse composed with itself, i.e. {{math|1=''f''<sup> −2</sup>(''x'') = ''f''<sup> −1</sup>(''f''<sup> −1</sup>(''x''))}}. Fractional negative iterates are defined analogously to fractional positive ones; for example, {{math|''f''<sup> −1/2</sup>(''x'')}} is defined such that {{math|1=''f''<sup> −1/2</sup>(''f''<sup> −1/2</sup>(''x'')) = ''f''<sup> −1</sup>(''x'')}}, or, equivalently, such that {{math|1=''f''<sup> −1/2</sup>(''f''<sup> 1/2</sup>(''x'')) = ''f''<sup> 0</sup>(''x'') = ''x''}}.
