I'm new to relational algebra and I need some help.

Let's say that I have 10 numbers : 1, 2, 3, 4.....9,10 which represent underground stations. How can I find which stations are close to station 8 (the answer should be 7 and 9).

The only comparisons that I know in RA are <, >, =, <=, >=, <>.

Can I have the above result (7,9) by using only these operations???

Thanks in advance