The functionality of Otherwise.

[lathlee]

Isn't usage of Otherwise in LSAT typically function as equivalent: If and Only if aka:

cuz typical pattern in LSAT in Otherwise: If we go movie, then we will have a fun; otherwise, we will not have fun.
Diagrram version would be: A B otherwise -A -B (contrapositive B A)

when the word, otherwise, is used in LSAT, the test makers test our understanding in such a manner by in a question stem state by -A or -B is given, what would occur in LG or LR Qs.

[Jon Denning]

It's always about the context of what's specifically being said, but in the movie example you give yes it'd be a double arrow.

What I mean is that the double arrow relationship depends on a reuse of the exact term (negated), and not something new, like: "If we go to the movies we'll have fun, otherwise we'll watch tv," as that would be:

Movies Fun
Not Movies TV (and Not TV Movies, and thus Fun)

So it depends on how it's presented. But otherwise could certainly yield a double arrow, yes.