You must buy a mathematically optimal sofa.

Proof:

Doing something other than what is optimal is suboptimal.

Doing something that is suboptimal is bad.

You must not do things that are bad.

Buying a mathematically optimal sofa is optimal.

Not buying a mathematically optimal sofa is suboptimal.

Not buying a mathematically optimal sofa is bad.


∴ You must by a mathematically optimal sofa.


Q.E.D.