type a_recd = {x: int; y: int; a:int}
type z_recd = {x: int; y: int; z:int}

type a      = Atype of a_recd
type z      = Ztype of z_recd

let v1 = Atype  {x=1;y=2;a=3}
let v2 = Ztype ({x=4;y=5;z=7} : z_recd)
;;