bsplinecurve b1 3 3 0 4 3 1 4 4  0 0 0 1  1 2 0 1   2 3 0 1  3 2 0 1   4 0 0 1
copy b1 result
smirror result 0 0 0 0 -1 1 
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pl
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set length 6.6067715112002166