fixes #1733 (`ln_eq0`) #1065

Job	Run time
rocq-core	46s
coq	43s
mathcomp-analysis-single	13m 58s
mathcomp-classical	2m 43s
mathcomp-reals	1m 55s
mathcomp-experimental-reals	1m 40s
mathcomp-reals-stdlib	1m 24s
mathcomp-analysis	12m 19s
mathcomp-analysis-stdlib	1m 29s
ssprove	5m 41s
	42m 38s

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