; element-wise subtraction of two blocks. e.g.
; vsub [1 2 3] [1 2 3] ; [0 0 0]
vsub: function [u v][
    map couple u v 'pair -> pair\0 - pair\1
]

differences: function [block][
    order: attr "order"
    if order = null -> order: 1
    loop 1..order 'n -> block: vsub block drop block
    return block
]

print differences .order: 4 [90.5 47 58 29 22 32 55 5 55 73.5]
print differences [1 2 3 4 5 6 7]