Helium 3 has a more complicated evolution than any of the other light elements. Since it is destroyed in some stellar processes, and most of the deuterium destroyed is made helium 3 unraveling the abundance can be confusing. One standard answer to this is to look for the current value of deuterium plus helium 3 as a possible bound on the deuterium abundance. This is more an attempt to avoid the need for a primordial abundance of helium 3 than to find an upper limit to that abundance.

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