( scratchpad ) { { 1 2 } { 2 3 } { 5 8 } { 4 6 } { 10 12 } } 7000000 { 14 18 } append [ seq-overlaps? . ] curry time t ==== RUNNING TIME 0.0 seconds ! the mistake was that find was indeed stopping at the fourth item, but until that item, it was matching against all of the huge 'rest'. compares 1 to rest, 2 to rest, etc. ! so now, I only use find on the short list of accumulated heads, which was what I actually meant to do.