SWI-Prolog -- function lgamma/1

Documentation
- Reference manual
  - Built-in Predicates
    - Arithmetic
      - General purpose arithmetic
        
        Arithmetic Functions
        
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        nan/0
        
        cputime/0
        
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        getbit/2
- Packages

Availability:Arithmetic function (see is/2)

lgamma(+Expr)

Return the natural logarithm of the absolute value of the Gamma function.^{124Some interfaces also
provide the sign of the Gamma function. We cannot do that in an
arithmetic function. Future versions may provide a predicate
lgamma/3 that returns both the value and the sign.}