add gitignore
Merge branch 'master' into dev
finish the check for assertion after 4
fix the error of using 'v' while there is a 'v' in params, use v' instead
finish the checking of assertion after line 5 & 6 in update()
fix the error of using "x.f |-> old" directly, it may not be the case
fix a error with respect to rely (12) of mutator thread
add the check for assertion "after 7" in Update()