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There is a newer version: 3.2.1

#
# Find Friday 13rd prime years 20th Century
#
prefix cal: 
select ?day  where {

bind (unnest(mapmerge(xt:span, mapselect(xt:prime, xt:iota(1901, 2000)))) as ?day)
               
function xt:span(?y) {
    mapselect (xt:check, "Friday", maplist(cal:date, ?y, xt:iota(1, 12), 13))
}

function xt:check(?d, ?x) {
 xt:day(?x) = ?d
}
                 
}