integrate=: adverb define
'a b steps'=. 3{.y,128
size=. (b - a)%steps
size * +/ u |: 2 ]\ a + size * i.>:steps
)
rectangle=: adverb def 'u -: +/ y'
trapezium=: adverb def '-: +/ u y'
simpson =: adverb def '6 %~ +/ 1 1 4 * u y, -:+/y'