In that case, if a line that is considered a side line starts getting played much more (because some super GM plays it or whatever), at what point does that become the main line, and what becomes of the original main line?
How does a line become a main line?
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How does a line qualify as the main line of an opening? Can there be more than one main line for an opening? If a sideline is considered a stronger line after more theory is developed on it, can it be promoted to the main line? How does it work?