The transformation of Galileo is a one-way transformation, i.e., it uses only the one-way speed of light, which for simplicity is assumed to be instantaneous. The transformation of Lorentz is a the two-way transformation, which uses the universal two-way speed of light. The following approach defines two different one-way transformations, which combine to equal the two-way Lorentz transformation. Note that *β* = *v*/*c*; 1/*γ*² = 1 − *β*²; and *γ* = 1/*γ* + *β*²*γ*.

Galilean transformation:

Dual Galilean transformation:

These could be combined with a selection factor *κ* of zero or one:

Lorentz transformation (boost): .

General Lorentz boost (see *here*):

with and *k* = 1/*c* for the Lorentz boost.

General dual Lorentz boost:

with and *k* = 1/*c*.