@Article{MT48,
    Author       = "McKinsey, J. and Tarski, A.",
    Year         = "1948",
    Title        = "{Some Theorems about the Sentential Calculi of Lewis and
                    Heyting}",
    Journal      = "Journal of Symbolic Logic",
    Volume       = "13",
    Number       = "1",
    Pages        = "1-15",
    Comment      = "TPTPRef"
}