How to get the CMOS inverter's open-loop gain
This is a typo in the 74LVC1GU04 datasheet. Open-loop gain GOL in the equation is listed at AOL=20(typical) in the second to last line about ZL>10kohm. Refer to the parent device http://www.nxp.com/documents/data_sheet/74HCU04.pdf which is the hex version of this (newer) single unbuffered inverter.