Channel capacity is additive over independent channels.[4] It means that using two independent channels in a combined manner provides the same theoretical capacity as using them independently. More formally, let p 1 {\displaystyle p_{1}} and p 2 {\displaystyle p_{2}} be two independent channels modelled as above; p 1 {\displaystyle p_{1}} having an input alphabet X 1 {\displaystyle {\mathcal {X}}_{1}} and an output alphabet Y 1 {\displaystyle {\mathcal {Y}}_{1}} .