  It is shown that calculus can apply on a fractal structure with the condition
that the infinitesimal limit of change of the variable is larger than the lower
cut-off of the fractal structure, and an assumption called local
decomposability. As an application, it is shown that the angular projection of
a fractal distribution in 3-dimensional space is not homogeneous at
sufficiently large angles. Therefore the angular projection of galaxy
distribution for sufficiently large angles can discriminate the fractal and the
homogeneity pictures.
