  The scalar one-loop 4-point function with one massless vertex is evaluated
analytically by employing the loop regularization method. According to the
method a characteristic scale $\mu_{s}$ is introduced to regularize the
divergent integrals. The infrared divergent parts, which take the form of
$\ln^{2}(\lambda^{2}/\mu^{2}_{s})$ and $\ln(\lambda^{2}/\mu^{2}_{s})$ as
$\mu_{s}\rightarrow 0$ where $\lambda$ is a constant and expressed in terms of
masses and Mandelstam variables, and the infrared stable parts are well
separated. The result is shown explicitly via $44$ dilogarithms in the
kinematic sector in which our evaluation is valid.
