If a mathematician.....

[Panicmode1]

Is a professional one, would that make them a "practising mathematician" or a "practicing mathematician"?

DH and I are in opposite camps...!

practising.

To practise - verb
A practice - noun

practice is a noun
practise is a verb.
hence practising.
Of the piano: do your piano practice.
Practise the piano.
Of maths:
Math's practice
Practising maths.

Practise is the verb

Practice is the noun

They are a practising mathematician running a successful mathematician's practice (using your example)

waaa! ignore mad apostrophe!!
Gets coat, leave pedants' corner and never returns.

Yay - I win!

It's on the 'blurb' which has come home from school today after a maths day run by the local outstanding school. It is in the first sentence of the first paragraph, and the rest of the flyer goes on about how outstanding the school is...not impressed!!

It's practicing in American English.

There's another thread on this subject. Substitute 'advise' and 'advice' to see which sounds right - the verb (-ise) or the noun (-ice). So here you'd be a practising mathematician. Easy!

Talking of which, have you seen that Singapore Maths Question that went viral recently? I literally could not focus on the maths question because the grammar was so bad:

"I don't know when Cheryl's birthday is, but I know that Bernard does not know too"
"At first I don't know when Cheryl's birthday is, but I know now".

I thought it was a play on words with "too" and "two".

I guess that's because the viral thing probably wasn't written by a native speaker.

Many kids in Singapore are educated in English; those at whom the question was aimed obviusly are. Not being a native speaker is no excuse. Or you think it's OK to educate people in bad English?

As an English teacher, of course not. I'd soon be out of a job.

However, the difference for non-native speakers between "too" and "either" is often very problematic as in many languages there is no distinction.

Weird. When I was learning languages, the bits I was best at were the bits that had no parallel in English, so you just had to learn the rules, like the French verbs that took etre (can't do diacritics) in the perfect tense. But then I suppose such things do appeal to pendants!

It's not just "too" and "either" though, it's also the use of the present instead of the past tense in the second line. tenses are pretty basic stuff and, as I understand it, the whole sequence of the order in which each character came to know certain information was pretty crucial to solving the problem. Therefore it would have been nice if they had got someone to check the English.