expression
not so; not like that
A negative form of そうだ, used to deny a preceding statement or assumption. Often appears in conditional phrases like そうでない場合 (if that is not the case).
See also: そうでない場合は
彼は忙しいと言ったが、実際はそうでない。
He said he was busy, but actually that's not the case.
そうでない場合は、もう一度やり直してください。
If that's not the case, please try again.