The second mapping            Ab
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NB. Construct the map that takes F0 to F2
   g2i =. F2 & builderi

NB. A composition
   g21 =. g2i @ g1
NB. Verfiy that F1 is mapped to F2
   (norm F2) matches g21 F1             NB.  TA DA !
1
NB.  Some examples applying the function:
     g21 1 2 3
0.026178 0.078534 1
   g21 7 8 9
0.0954198 0.114504 1
   g21 10 0 0
_1.25 0 1
   g21 8 0 1
10 0 1
   g21 9 0 1
1 0 0

