Using IF function with Multiple Criteria
 

I have a workbook with three sheets, data in each, and I need to create a formula to use in the first sheet that will check if certain criteria are met from the other two sheets, a value may be entered. For example,

Sheet 1:
In A4, I want to enter a numerical value such as 2.0123
In B4, it will either be "L" or "R"

I would like to create a formula, conditional I think, that will check - Sheet 1 against the numerical valeus stored in Sheet 2 and 3
IF B4 equals "L", then the value entered in A4 must be greater than Sheet 2 B4 (2.0122)
if not, then the value cannot be enterred into the cell.
Likewise, if the value in B4 is "R" in Sheet 3

If B4 is "R", value in A4 must be greater than 2.0122

Can this be done?

Any/all assistance will be greatly appreciated.