Coverings of internal groupoids and crossed modules in the category of   groups with operations
  In this paper we prove some results on the covering morphisms of internal groupoids. We also give a result on the coverings of the crossed modules of groups with operations. 
H. Fulya Ak{\i}z and Nazmiye Alemdar and Osman Mucuk and Tun\c{c}ar   \c{S}ahan
math.CT math.AT