What does this curve over the C-B bond mean?

[![enter image description here](https://i.stack.imgur.com/cgNXg.jpg)](https://i.stack.imgur.com/cgNXg.jpg)


I have come across this notation in a question I am trying to answer and am unsure of what exactly it means, can anyone clarify what this represents?




That ‘curve’ is a bracket, and the whole thing is a shorthand notation for ‘two of the same group’.


Thus, the molecule could be termed *bis-(3-methylbut-2-yl)borane*.


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