The vary long run
The time period over which technology might change. It is likely that technical change is biased towards to productivity of particular factors. For example, more efficient machinery may be developed, or more efficient ways of motivating and utilising labour. Any given combination of capital and labour would now produce a higher level of output, or the same output could be produced using relatively fewer factors. As noted above, or the firm should now orientate production towards those factors which have relatively more productive.
We can now analyse production and cost under each of the above time periods.