@Article{RG04-JFM,
    Author       = "Romanowicz, K. and Grabowski, A.",
    Year         = "2004",
    Title        = "{The Operation of Addition of Relational Structures}",
    Journal      = "Journal of Formalized Mathematics",
    Volume       = "12",
    Number       = "3",
    Pages        = "335-339",
    Comment      = "TPTPRef,LATSUM_1"
}