(a) if the vendor or lessor has subsequently to the contract acquired any interest in the property, the purchaser or lessee may compel him to make good the contract out of such interest;

(b) where the concurrence of other persons is necessary for validating the title, and they are bound to concur at the request of the vendor or lessor, the purchaser or lessee may compel him to procure such concurrence, and when a conveyance by other persons is necessary to validate the title and they are bound to convey at the request of the vendor or lessor, the purchaser or lessee may compel him to procure such conveyance;

(c) where the vendor professes to sell unencumbered property, but the property is mortgaged for an amount not exceeding the purchase money and the vendor has in fact only a right to redeem it, the purchaser may compel him to redeem the mortgage and to obtain a valid discharge, and, where necessary, also a conveyance from the mortgagee;

(d) where the vendor or lessor sues for specific performance of the contract and the suit is dismissed on the ground of his want of title or imperfect title, the defendant has a right to a return of his deposit, if any, with interest thereon, to his costs of the suit, and to a lien for such deposit, interest and costs on the interest, if any, of the vendor or lessor in the property which is the subject- matter of the contract.