[tex-k] MFbook: issue with exercise 9.1 (pair+numeric)

[Karl Berry]

        lft z21 = rt z20 + 1
        ! Not implemented: (pair)+(known numeric).

    Maybe it would be more correct to use the following?
        lft z21 = rt z20 + (1,0)

Thanks, the correction looks right to me. Added to newbug. -k