Let $W$ denote the set of all positive definite binary quadratic forms, with integer coefficients, and having discriminant $-67$. Let $S L_{2}(\mathbb{Z})$ be the group of all $2 \times 2$ matrices with integer entries and determinant 1. Prove that $W$ is infinite, but that all elements of $W$ are equivalent under the action of the group $S L_{2}(\mathbb{Z})$