Make uses of Arguments more rubust.

See also Coq bug #5712.
4 jobs for master in 6 minutes and 33 seconds
Status Job ID Name Coverage
  Test
passed #3229
fp-timing
stdpp-coq8.5.3

00:02:23

passed #3228
fp-timing
stdpp-coq8.6

00:02:02

passed #3227
fp-timing
stdpp-coq8.6.1

00:02:00

passed #3226
fp-timing
stdpp-coq8.7

00:04:57