timing arc and unateness

[kramerny]

Hi guys,
Can some one let me know the use of unateness in .lib*. like and has positive-unate because a rising input will produce a rising output.

How is this going to help in timing?

 

[chiplogic]

Unateness is important for timing as it specifies how the edges (transitions)
can propagate through a cell and how they appear at the output of the cell.
This information will be used by STA tool to track worst/best paths in a given timing path