  It is known that if $M,\,N$ are continuous two-variable means such that
$|M(x,y)-N(x,y)| < |x-y|$ for every $x,\ y$ with $x\ne y$, then there exists a
unique invariant mean (which is continuous too).
  We are looking for invariant means for pairs satisfying the inequality above,
but continuity of means is not assumed.
  In this setting the invariant mean is no longer uniquely defined, but we
prove that there exist the smallest and the biggest one. Furthermore it is
shown that there exists at most one continuous invariant mean related to each
pair.
