Coding the real locus of X_0+(N)
  Let X_0+(N) be the Atkin-Lehner quotient of the modular curve X_0(N) associated to the Fricke involution wN. Assume N > 3 prime and endow the real locus X+ 0 (N)(R) with the real topology. In this paper we revisit a special case of result due to Ogg on the connected components of X_0+(N)(R). Then we obtain a formula for the homology class of each connected component of X_0+(N)(R) in terms of Manin symbols. 
Carlos Castano-Bernard