Request to checkVenn diagram issue solve by Unix programm

Hello

Any Unix programm can help me to solve thsi issue:

I have 2 venn digrams please checke the attached file for pictures of venn diagram for eg red is A yellow is B and green is C..Please see attached file for Venn diagrams

In one .....
I have 3 data set

A , B and C

Venn diagram between A and B
shows:

A = 13+2098
B =2098+27079

now in venn diagram between A and B there are 2098 common entries

but in venn diagram between A B and C:there are only 2097 entries common in A and B(including those whichare common between A , B and C is there somethign wrong why its happening?pease explain can it be explained using Unix programm.