  The fastest quantum algorithms (for the solution of classical computational
tasks) known so far are basically variations of the hidden subgroup problem
with {$f(U[x])=f(x)$}. Following a discussion regarding which tasks might be
solved efficiently by quantum computers, it will be demonstrated by means of a
simple example, that the detection of more general hidden (two-point)
symmetries {$V\{f(x),f(U[x])\}=0$} by a quantum algorithm can also admit an
exponential speed-up. E.g., one member of this class of symmetries
{$V\{f(x),f(U[x])\}=0$} is discrete self-similarity (or discrete scale
invariance). PACS: 03.67.Lx, 89.70.+c.
