public static Func <TA?, TB> IfMapUnsafeN <TA, TB>(TA v, Func <TA, TB> f)
     where TA : struct
 {
     return(IfMapUnsafeN <TA, TB>(v)(f));
 }
 public static Func <TA?, TB> IfMapUnsafeN <TA, TB>(Func <TA, bool> p, Func <TA, TB> f)
     where TA : struct
 {
     return(IfMapUnsafeN <TA, TB>(p)(f));
 }