What is unilateral mistake? Which of the following is correct?

Where one party is mistaken there is unilateral mistake since the other party is not mistaken and consequently the contract is still enforceable (unless one party was aware of the other's mistaken belief

Unilateral mistake refers to small mistakes made by a party, which cannot affect the validity of a contract

Where one party makes a substantial mistake, as distinct from a small mistake, then the contract must come to an end

unilateral mistake is the same as mutual mistake, essentially there is no contract that can be enforced