flow2<A, B, C>  function 
 
- B ab(- A
 
- C bc(- B
 
Implementation
C Function(A) flow2<A, B, C>(B Function(A) ab, C Function(B) bc) =>
    (A a) => pipe3(a, ab, bc);C Function(A) flow2<A, B, C>(B Function(A) ab, C Function(B) bc) =>
    (A a) => pipe3(a, ab, bc);