CREATE FUNCTION ufn_IsWordComprised (@setOfLetters VARCHAR(20), @word VARCHAR(20))
RETURNS BIT
AS
BEGIN
    IF (SUBSTRING(@word,1,1) LIKE '[' + @setOfLetters + ']')
    BEGIN
        SET @word = SUBSTRING(@word,2,LEN(@word)-1)
        RETURN dbo.ufn_IsWordComprised (@setOfLetters,@word)
    END

    IF (LEN(@word) = 0)
        RETURN 1
    RETURN 0
END