 Chaitin has defined Chaitin's constant Ω, a real number whose digits are equidistributed and which is sometimes informally described as an expression of the probability that a random program will halt.Ω has the mathematical property that it is definable, with asymptotic approximations from below (but not from above), but not computable.Chaitin is also the originator of using graph coloring to do register allocation in compiling, a process known as Chaitin's algorithm.