IF YOU CAN SEE THIS go to http://www.cs.cornell.edu/Info/People/sfa/Nuprl/Shared/Xindentation_hack_doc.html
At:
msg-form-join-list L:MsgA List. (L) MsgAForm
By:
InductionOnList THEN Unfold `ma-join-list` 0 THEN Reduce 0
THEN
Try (Fold `ma-join-list` 0)