:: gregorian-easter ( year -- month day )
    ! note, the definition isn't legal should have lots of [ f ]
    [let | a! b! c! d! e! f! g! h! i! k! l! m! n! p! |
        year 19 rem                      a!
        year 100 /mod                    b! c!
        b 4 /mod                         d! e!
        b 8 + 25 /i                      f!
        b f - 1+ 3 /i                    g!
        19 a * b + d - g - 15 + 30 rem   h!
        c 4 /mod                         i! k!
        32 2 e * + 2 i * + h - k - 7 rem l!
        a 11 h * + 22 l * + 451 /i       m!
        h l + 7 m * - 114 + 31 /mod      n! p!
        n p 1+ ;