Typos in ob.txt

[orcmid]

Another typo in obtheory (Q: shall I just put all typos into this issue?):

Lines 33,34:
* There are two selector functions, ob.a(z) and ob.b(z) that given
any ob and determine an ob as their result.

"given any ob determine an ob ...." -- the "and" does not belong there.

Originally posted by @band in #16 (comment)

[band]

obtheory typo, lines 107-111:

Ob5. Totality
ob.is-individual(z) ∨ ob.is-enclosure(z) ∨ ob.is-pair(z)

    It is a consequence that each ob is exactly one of pair,

enclosure, and individual and there are no others.

Should this read "... one of pair, enclosure, or individual and ..."?

[band]

obtheory typo, line 139

In formats having greater typographical flexibility than plaintest, there

"plaintest" should be "plaintext"