Semicomputable function
（重定向自Semicomputable）
In computability theory, a semicomputable function is a partial function 
that can be approximated either from above or from below by a computable function.
More precisely a partial function is upper semicomputable, meaning it can be approximated from above, if there exists a computable function 
, where 
is the desired parameter for 
and 
is the level of approximation, such that: