/usr/bin/lablgl is in liblablgl-ocaml-dev 1:1.05-2.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 | #!/bin/sh
# toplevel with lablGL and Togl
exec ocaml -I +labltk -I "/usr/lib/ocaml/lablgl" lablgl.cma labltk.cma togl.cma $*
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