  We offer a solution to the long-standing problem of group completing within
the context of rig categories (also known as bimonoidal categories). Given a
rig category R we construct a natural additive group completion R' that retains
the multiplicative structure, hence has become a ring category. If we start
with a commutative rig category R (also known as a symmetric bimonoidal
category), the additive group completion R' will be a commutative ring
category. In an accompanying paper we show how this can be used to prove the
conjecture from [BDR] that the algebraic K-theory of the connective topological
K-theory spectrum ku is equivalent to the algebraic K-theory of the rig
category V of complex vector spaces.
