Who owns all of the land in a given area, even if he "gives" it to a
lord to use?

Explanation: The legal owner of the property (trustee) has the right to possession, the privilege of use, and the power to convey those rights and privileges. The trustee thus appears by all counts to be the owner of the property—or so it appears to all but one person, the beneficial owner (beneficiary, cestui que trust).

for this case we have the following equation:

we apply distributive property to the terms within parentheses.

subtracting 2 on both sides of the equation: