Validity of a bequest concerning a portion of the income (Ghalla) of a house?

Primary text

A bequest specifying a Dinar from the income of a house is valid, even if the total income amounts to two Dinars. If the heirs wish to sell half the house while retaining the half whose income is designated as the Dinar bequest, the legatee (Mawsa lahu) has the right to prevent the sale of that specific portion, as it is possible that the rent assigned to that half might be less than one Dinar. If the entire house's income does not exceed one-third of the estate value, the heirs may sell the portion exceeding the one-third allowance, but they must preserve the one-third portion for the bequest.