If a person is only interested in number theory, then he/she would just want to access only a few tags, such as number theory, elementary number theory, diophantine equation, etc. But if we select both “number-theory” and "elementary-number-theory" tags, then we will get the posts which tag both “number-theory” and "elementary-number-theory" :
663
questions tagged
(number-theory) (elementary-number-theory)
So the relationship between them is "and", I'd like to search the post which tag is "number-theory " or "elementary-number-theory", hence the relationship between them is "or", I wonder if one can do this ?