tractability
it has become customary to speak of problems that are solvable, not only in principle but also in practice, as tractable; problems that may be solvable in principle but are not solvable in practice are then called intractable.
the problem of determining membership of strings in a given broken link: blk:def-lang 
is tractable if and only if 
.
[cite:;taken from @computability_davis_1994 theorem 2.1]
[cite:;taken from @computability_davis_1994 chapter 15 polynomial-time computability] is tractable if and only if .[cite:;taken from @computability_davis_1994 theorem 2.1]