#define F1(f)   A f(    A w)
#define F2(f)   A f(A a,A w) 
#define DF1(f)  A f(    A w,A self)
#define DF2(f)  A f(A a,A w,A self)

extern DF1(folk1);

folk1(y,S)
  ┌───┬─────┬─────┬─┬─┬─┬────┬─┬─┬─┬────┬──┐
S │HDR│folk1│folk2│a│b│c│flag│_│_│_│fdep│fk│
  └───┴─────┴─────┴─┴─┴─┴────┴─┴─┴─┴────┴──┘
      ┌───┬──────┬──────┬─┬─┬─┬────┬─┬─┬─┬────┬──┐
a     │HDR│reduce│oprod │d│0│0│flag│_│_│_│fdep│/ │
      └───┴──────┴──────┴─┴─┴─┴────┴─┴─┴─┴────┴──┘
...