src/main/java/com/basistech/tclre/Compiler.java
private void markst(Subre t) {
        assert t != null;

        t.flags |= Subre.INUSE;
        if (t.left != null) {
            markst(t.left);
        }
        if (t.right != null) {
            markst(t.right);
        }
    }
private void markst(Subre t) {
        assert t != null;

        t.flags |= Subre.INUSE;
        if (t.left != null) {
            markst(t.left);
        }
        if (t.right != null) {
            markst(t.right);
        }
    }
markst - mark tree nodes as INUSE