OA article - HD 3/4/17.  
Green in Sherpa: Author's Pre-print: 	green tick  author can archive pre-print (ie pre-refereeing)
Author's Post-print: 	green tick  author can archive post-print (ie final draft post-refereeing)
Publisher's Version/PDF: 	green tick  author can archive publisher's version/PDF
General Conditions:  Author's pre-print and Author's post-print on author's personal website, institutional repository, arXiv or preprint servers only
    Publisher copyright must be acknowledged
    Must link to publisher version
    Publisher's version/PDF may be used on author's personal website only
    Publisher's version/PDF cannot be used in a repository
    Authors may have deposit in funding body's archive or funding body's designated repository for public release 6 months after publication or immediately upon payment of fee
    All PNAS-formatted versions are deposited in PubMed Central for release after 6 months, regardless of funding. - General conditions states: Publisher's version/PDF cannot be used in a repository, 'Free content only', 12.4.17--MMM