Array lookup

Hello,
I was wondring if there was a formula to do this in excel. I have the data in two columns, col a and col b
What I want excel to check first is if there are any values in col A thst are repeating themselves. If there are any then it should take all those values and check their adjacent cells in col B for further conditions.
So I could have my data listed like this
A B
a 1
a 2
a 7
b 4
b 5
c 6
So in the first case the first condition is met as "a" repeats thrice.it should now check all values correponding to "a" and if any one value is less than 2 and any other value is greater than 5 it should give me true.so in the first case it should give me true as the value corresponding to first "a" is less than 2 and the value corresponfing to third "a" is greater than 5 .However for b it should return false as neither of the two conditions are met.Hope I have explained this well.Will appreciate any responses on this .