CriteriaValue  - преобразование (CriteriaValue to NullableDouble)

public static implicit operator double? (
	CriteriaValue value
)

Public Shared Widening Operator CType ( 
	value As CriteriaValue
) As Double?

static implicit operator Nullable<double> (
	CriteriaValue^ value
)

F# не поддерживает объявление новых операторов приведения.