Specification

P40 (**) Goldbach's conjecture.
       Goldbach's conjecture says that every positive even number greater
       than 2 is the sum of two prime numbers. Example: 28 = 5 + 23. It is
       one of the most famous facts in number theory that has not been proved
       to be correct in the general case. It has been numerically confirmed
       up to very large numbers (much larger than we can go with our Prolog
       system). Write a predicate to find the two prime numbers that sum up
       to a given even integer.

Example

> say ~goldbach 28
    5 23

use v6;



subset Even of Int where * %% 2;

sub goldbach (Even $n where * > 2 ) {
    for 2..$n/2 -> $k {
        if $k.is-prime && ($n-$k).is-prime {
            return ($k, $n-$k);
        }
    }
    return; # fail
}

say ~ goldbach $_ for 28, 36, 52, 110, 62710560;

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