; data on languages from Sebesta's book, and other sources
(infer (language fortran-1 1957))
(infer (language flow-matic 1957))
(infer (language flpl 1957))
(infer (language algol-58 1958))
(infer (language fortran-2 1958))
(infer (language comtran 1958))
(infer (language algol-60 1960))
(infer (language cobol 1960))
(infer (language lisp 1960))
(infer (language fortran-4 1962))
(infer (language cpl 1963))
(infer (language apl 1963))
(infer (language simula-1 1964))
(infer (language basic 1964))
(infer (language pl-1 1965))
(infer (language algol-w 1966))
(infer (language simula-67 1967))
(infer (language algol-68 1968))
(infer (language bcpl 1969))
(infer (language b 1970))
(infer (language pascal 1971))
(infer (language c 1972))
(infer (language prolog 1973))
(infer (language clu 1975))
(infer (language scheme 1975))
(infer (language fortran-77 1977))
(infer (language green 1979))
(infer (language smalltalk-80 1980))
(infer (language ada 1983))
(infer (language common-lisp 1984))
(infer (language cplusplus 1985))

(infer (parent fortran-1 fortran-2))
(infer (parent fortran-1 algol-58))
(infer (parent algol-58 algol-60))
(infer (parent flow-matic cobol))
(infer (parent comtran cobol))
(infer (parent fortran-2 fortran-4))
(infer (parent algol-60 basic))
(infer (parent fortran-4 basic))
(infer (parent algol-60 pl-1))
(infer (parent fortran-4 pl-1))
(infer (parent cobol pl-1))
(infer (parent algol-60 simula1))
(infer (parent simula1 simula-67))
(infer (parent simula-67 smalltalk-80))
(infer (parent algol-60 algol-w))
(infer (parent algol-w pascal))
(infer (parent pascal green))
(infer (parent green ada))
(infer (parent pascal clu))
(infer (parent algol-68 clu))
(infer (parent algol-60 algol-68))
(infer (parent fortran-4 fortran-77))
(infer (parent cpl bcpl))
(infer (parent bcpl b))
(infer (parent b c))
(infer (parent algol-68 c))
(infer (parent c cplusplus))
(infer (parent smalltalk-80 cplusplus))
(infer (parent lisp scheme))
(infer (parent algol-60 scheme))
(infer (parent scheme common-lisp))


(infer (ancestor L1 L2) from (parent L1 L2))
(infer (ancestor L1 L2) from (parent L3 L2) (ancestor L1 L3))