M_air                   M_air
M_air_excl              m_air
M_excl                  M_excl
nps.invalid             M_Invalid
nps.necessary           testIc
nps.test                Main function of the package.
nps.valid               nps.valid
product_fraction        Reduces out factors of fraction of products and
                        calculates the fraction Analog to
                        prod(num)/prod(den)
