[PRD] todo before wd2 publication

todo on prd before wd2

proposed

sure
- add/check references and links;
- add squares at the end of defs
- change the semantics of actions from entailment to addition/soustraction
- editors note on actions
- preamble on fact base
- preamble on group
- update def on matching substitution, to fit modified def of condition satisfaction

maybe
- example

all the comments from hassan that really address issues in bld are pending and will not be taken into account for wd2

christian