let n2 = Array.length b in
let n3 = Array.length c in
if n1 = n2 && n1 = n3 then Array.init n1 (fun i -> f a.(i) b.(i) c.(i))
let n2 = Array.length b in
let n3 = Array.length c in
if n1 = n2 && n1 = n3 then Array.init n1 (fun i -> f a.(i) b.(i) c.(i))