[isabelle] Inequalities on real numbers: How to use "(x::real) > 0 --> x >= 0"?



Dear Isabelle experts,

somewhere in a proof that involves real numbers from the theory "Real" I would like to infer "(x::real) >= 0" from "x > 0".

For now I solved the problem by introducing the following axiomatic "lemma":

lemma greater_zero_implies_greater_equal_zero [simp] :
  fixes x::real
  assumes "x > 0"
  shows "x ≥ 0"
sorry

(Note that I am new to Isabelle, so there might be better ways of doing this.)

I would be interested in some built-in rule, or a theory in the library, that would simply do this inference for me.

I am less interested in writing my own proof of this in place of the "sorry" above, as my overall formalisation is a higher-level applied one.

Cheers, and thanks in advance for any help,

Christoph

--
Christoph Lange, School of Computer Science, University of Birmingham
http://cs.bham.ac.uk/~langec, Skype duke4701

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