Do I need to to hyphenate:
"It is a locally-injective mapping."
where I use locally injective as a term--a concept:
"This mapping is locally injective."
For example, it is defined in:
[Weber14 "Locally Injective Parametrization with Arbitrary Fixed Boundaries"]
Adding some links regarding hyphenating the adverb 'well', which may be relevant:
A Well-Known Problem: Hyphens With “Well” Words https://www.businesswritingblog.com/business_writing/2009/07/a-wellknown-problem-well-known.html
Well-Hyphenated Compound Adjectives https://www.btb.termiumplus.gc.ca/tpv2guides/guides/favart/index-fra.html?lang=fra&lettr=indx_autr8O0GT3FD1GuY&page=9p1twFAGORMI.html
"The elements of style" by Strunk and White says:
"When two or more words are combined to form a compound adjective, a hyphen is usually required."
The wiki page is quite comprehensive and sounds convincing: