\usemodule[bib]

\unprotect

\newcount\bibrefsep

\def\bibinsertrefsep
 {\advance\bibrefsep\plusone
  \ifconditional\firstbibrefsep
    \setfalse\firstbibrefsep
   \else \ifnum\bibrefsep=\bibitemcounter\relax
       \bibrefsep=0
       \bibalternative\c!lastpubsep
   \else
       \bibalternative\c!pubsep
   \fi
  \fi }

\def\dobibauthornumref#1%
 {\bibinsertrefsep
  \doifbibreferencefoundelse{#1}
    {\begingroup
     \@EA\setcurrentbibauthor\@EA{\bibgetvara{#1}}%
     \currentbibauthor
     \bibalternative\c!inbetween
     \setuppublications[\c!refcommand=num]%
     \cite[#1]%
     \endgroup}
    {\unknownreference{#1}}}


\def\bibauthornumref[#1]%
  {\getcommalistsize[#1]%
   \global\bibitemcounter\commalistsize
   \bibresetrefsep
   \bibalternative\v!left
   \processcommalist[#1]\dobibauthornumref 
   \bibalternative\v!right }

\protect

\setuppublications[state=start,
                  sorttype=bbl,
                  refcommand=authornum,
                  numbering=yes]

\setupcite
       [authornum]
       [pubsep={, },
        lastpubsep={ and },
        andtext={ \& },
        compress=no,
        inbetween={: },
        left={(},
        right={)}]


\startpublication[k=gowpagegp,t=book,
a={{Gow},{Page}},y=1968,
n=5,s=GP68]
\author[]{A.~S.~F.}[A.~S.~F.]{}{Gow}
\author[]{Denys}[D.]{}{Page}
\pubyear{1968}
\title{The Greek Anthology{\em , 2} The Garland of Philip}
\city{Cambridge (Engl.)}
\pubname{Cambridge UP}
\stoppublication

\startpublication[k=gowpagegp2,t=book,
a={{Gxow},{Pxage}},y=1968,
n=5,s=GP68]
\author[]{A.~S.~F.}[A.~S.~F.]{}{Gxow}
\author[]{Denys}[D.]{}{Pxage}
\pubyear{1968}
\title{The Greek Anthology{\em , 2} The Garland of Philip}
\city{Cambridge (Engl.)}
\pubname{Cambridge UP}
\stoppublication

\setuppublicationlist[samplesize={VSdK90},totalnumber=1]

\starttext

\loggingall

\cite[gowpagegp]

\cite[gowpagegp,gowpagegp2]

\page

\placepublications[criterium=all]

\stoptext