What does the approximately equal sign mean in topology notation?

[ehrenfest]

Homework Statement

I saw the following statement in a proof that a second countable normal space is homeomorphic to the Hilbert cube:

$$n = (B_i, B_j)$$

where the = sign is replaced with an approximately equals which I do not know how to make in latex

B_i and B_j are basis sets s.t. B_i closure is a subset of B_j

n is a natural number

Anybody know what the the approximately equal sign means (they already defined what the ordered pair was)?

Homework Equations

The Attempt at a Solution

 

[matt grime]

\sim is what you might want.

 

[morphism]

Where did you see this? Can you give us a link, or book & page number?

By the way, you probably meant to say "homeomorphic to a subspace of the Hilbert cube".