assignment of states to all the vertices of T is called a configuration. The lit-only σ-game
allows the player to pick a lit vertex and change the states of all its neighbours. We prove
that for any initial configuration one can make a sequence of allowable moves to arrive at a
configuration in which the number of lit vertices is no greater than⌈ ℓ2⌉. We also give
examples to show that the bound⌈ ℓ2⌉ cannot be relaxed to⌊ ℓ2⌋.