[MichaelRo]

Well there is common stuff that one must be familiar with to be proficient and marginal stuff that you can get by without knowing because chances is you're not going to need it.

Like take for instance financial mathematics where I had some special interest, it's totally oblivious to areas such as geometry or number theory. I never had to figure out if a polynomial is divisible by 6 for instance :)

Like computer science, there's the common algorithms stuff but being an expert in web development doesn't help you much in writing high frequency trading server code, and the other way around.