Add definitions of the numbers 2 through 10.
Adds theorems to replace one part of an expression.

Signed-off-by: Paul Merrell <merrell42@gmail.com>
Merge branch 'master' of https://ghilbert-app.appspot.com/git
add structured comments to OrderedPairTheoremForwardFirst.
Reindent OrderedPairTheoremForwardFirst and revise structured comments.
Sent by Paul Merrell to the mailing list.
Fix LessEqualBuilder.
Fix LessThanLessEqualImplication.
Fix LessEqualLessThanTransitivity.
Fix LessEqualTransitivity.
Add formatting guidelines for mpg.
Merge branch 'master' of https://ghilbert-app.appspot.com/git
Merge branch 'master' of https://ghilbert-app.appspot.com/git
Add structured comments to format proofs into columns.
Commit from web thm editor: save sylbi2
Add titles and colored highlighting to theorems and axioms as structured comments.
Start in on proving the propositional logic in general from peano/prop.ghi.
Export the rest of the axioms.
Prove peano/prop.ghi from general/Classical_propositional_calculus.ghi.
Slight cleanups to the proof of the reverse.
Finish prop.gh through con2bii, which gets us to the start of the conjunction and disjunction section.
Add disjunction theorems through orass (and df-an).
Prove more disjunction theorems, through or4.