USING: kernel math sequences ; IN: euler.002 [ 3drop ] [ [ ?retotal next-fibs ] dip (sum-even-fibs-below) ] if ; PRIVATE> : sum-even-fibs-below ( max -- sum ) [ 0 0 1 ] dip (sum-even-fibs-below) ; : euler002 ( -- answer ) 4000000 sum-even-fibs-below ; MAIN: euler002