0 QTRS
active(c) → mark(f(g(c))) active(f(g(X))) → mark(g(X)) mark(c) → active(c) mark(f(X)) → active(f(X)) mark(g(X)) → active(g(X)) f(mark(X)) → f(X) f(active(X)) → f(X) g(mark(X)) → g(X) g(active(X)) → g(X)