Concerning the obstacle-problem-like equation ∆u where λ + 0 and λ + + λ − > 0, we prove regularity of the solution as well as an estimate on the Hausdorff dimension of the free boundary Ω ∩ (∂{u > 0} ∪ ∂{u < 0}). We apply this result to the Stefan-like equation α∂ t max(v, 0) + β∂ t min(v, 0) − ∆v = 0.