 Quantum logic treats the outcome of a quantum measurement as a logical proposition and studies the relationships and structures formed by these logical propositions.They are organized into a lattice, in which the distributive law, valid in classical logic, is weakened, to reflect the fact that in quantum physics, not all pairs of quantities can be measured simultaneously.The "representation theorem" in quantum logic shows that such a lattice is isomorphic to the lattice of subspaces of a vector space with a scalar product.