diff --git a/Programming/PORR/.gitattributes b/Programming/PORR/.gitattributes
deleted file mode 100644
index e42fe68c..00000000
--- a/Programming/PORR/.gitattributes
+++ /dev/null
@@ -1,3 +0,0 @@
-code/spd_5000.npz filter=lfs diff=lfs merge=lfs -text
-code/poli3_1.npz filter=lfs diff=lfs merge=lfs -text
-code/poli3_2.npz filter=lfs diff=lfs merge=lfs -text
diff --git a/Programming/PORR/code/spd_5000.npz b/Programming/PORR/code/spd_5000.npz
deleted file mode 100644
index 11b44646..00000000
--- a/Programming/PORR/code/spd_5000.npz
+++ /dev/null
@@ -1,3 +0,0 @@
-version https://git-lfs.github.com/spec/v1
-oid sha256:2aa92da25acfeafeb204ee81e2feafd04b39f3a86fad2765f538ab95e4581d96
-size 200041030
diff --git a/Programming/ZPOB/run.sh b/Programming/ZPOB/run.sh
index 0ad11059..3aa3c4bb 100755
--- a/Programming/ZPOB/run.sh
+++ b/Programming/ZPOB/run.sh
@@ -7,5 +7,11 @@ set -euo pipefail
 # shellcheck source=../../scripts/course_lib.sh
 . "$(dirname "$(readlink -f "$0")")/../../scripts/course_lib.sh"
 
-course_main --kind tex \
+# esej.tex ends with \bibliography{references} but contains no \cite and no
+# \bibliographystyle, so bibtex aborts and latexmk reports 12 -- after having
+# already written a correct esej.pdf. That is how the essay was handed in:
+# the submitted esej.pdf (LuaTeX, 2023-12-12) has no bibliography either.
+# Adding \bibliographystyle would print a References section that was never
+# part of the deliverable, so the build skips bibtex instead.
+course_main --kind tex --no-bibtex \
     -- "$@"
diff --git a/scripts/course_lib.sh b/scripts/course_lib.sh
index 52050655..46a1c47f 100644
--- a/scripts/course_lib.sh
+++ b/scripts/course_lib.sh
@@ -218,8 +218,20 @@ _run() {
             local dir base
             dir="$(dirname "$tex")"
             base="$(basename "$tex")"
+            # A document that declares \bibliography but never cites anything
+            # makes bibtex exit 2 ("I found no \citation commands"), and
+            # latexmk turns that into exit 12 even though the PDF is fine.
+            # --no-bibtex says "this one was handed in without a bibliography",
+            # which is a fact about the deliverable, not a suppression.
+            # An `x && y=1` one-liner would be a set -e landmine here: when x
+            # is false the list returns 1 and the whole runner exits.
+            local bibflag=()
+            if [[ -n "${COURSE_TEX_NO_BIBTEX:-}" ]]; then
+                bibflag=(-bibtex-)
+            fi
             if [[ $tool == latexmk ]]; then
-                ( cd "$dir" && latexmk -pdf -interaction=nonstopmode -outdir=build "$base" )
+                ( cd "$dir" && latexmk -pdf "${bibflag[@]}" \
+                    -interaction=nonstopmode -outdir=build "$base" )
             else
                 ( cd "$dir" && mkdir -p build \
                     && "$tool" -interaction=nonstopmode -output-directory=build "$base" )
@@ -320,12 +332,14 @@ course_main() {
     COURSE_ENTRY=""
     COURSE_NOTE=""
     COURSE_TEST_DIR=""
+    COURSE_TEX_NO_BIBTEX=""
     while [[ $# -gt 0 ]]; do
         case "$1" in
             --kind)  COURSE_KIND="$2"; shift 2 ;;
             --entry) COURSE_ENTRY="$2"; shift 2 ;;
             --note)  COURSE_NOTE="$2"; shift 2 ;;
             --test-dir) COURSE_TEST_DIR="$2"; shift 2 ;;
+            --no-bibtex) COURSE_TEX_NO_BIBTEX=1; shift ;;
             --) shift; break ;;
             *) break ;;
         esac