  Critical point of liquid-gas (LG) transition does not conform with the
paradigm of spontaneous symmetry breaking because there is no broken symmetry
in both phases. This stimulated the ongoing debate about the nature of the
universality class of the transition -- lasting since the creation of the
theory of scaling. We revisit the conjecture that the LG criticality is that of
the Ising model. Large scale Monte Carlo simulations of the LG criticality in
2D free space in combination with the numerical flowgram method give the
critical indices agreeing with the Onsager values within the error of 1\%. The
related problem about the role of higher order odd terms in the (real)
$\varphi^4$ field model is addressed too. The scaling dimension of the
$\varphi^5$ term at criticality is shown to be the same as of the linear one
$\varphi$. We suggest that the role of all higher order odd terms is simply in
generating the linear field operator at the criticality.

Statistical Mechanics