  Given an arbitrarily weak notion of left-<f>-porosity and an arbitrarily
strong notion of right-<g>-porosity, we construct an example of closed subset
of the real line which is not sigma-left-<f>-porous and is right-<g>-porous. We
also briefly summarize the relations between three different definitions of
porosity controlled by a function; we then observe that our construction gives
the example for any combination of these definitions of left-porosity and
right-porosity.
