unit p where
    signature H where
        data T

unit q where
    signature H where
        data T = T

unit pq0 where
    dependency p[H=<H>]
    dependency q[H=<H>]

unit pq1 where
    dependency p[H=<H>]
    dependency q[H=<H>]
    signature H where
        data T = T

unit pq2 where
    dependency p[H=<H>]
    dependency q[H=<H>]
    signature H where
        data T