# Re: Tagged formulas

I'm not sure what "works quite well".  To clarify things, if

Action(t) == t = y
Capture(var, Action(_)) == \E t \in {var} : t = var /\ Action(t)

Then

Capture(x, Action)' = (\E t \in {x} : t = x /\ (t=y))'
= (\E t \in {x'} : t' = x' /\ (t'=y'))
= (\E t \in {x'} : t = x' /\ (t=y'))

The last equality holds because t' = t, since \E t introduces t as a constant.

Leslie

On Thursday, January 7, 2016 at 2:42:51 PM UTC-8, Ron Pressler wrote:

BTW, your suggestion of \E t : t = x works quite well. At first I defined:

Capture(var, Action(_)) == \E t \in S : t = var /\ Action(t) \* S is a constant set known to contain the variable var

and it does the capture/lowering I want.

Then I tried:

Capture(var, Action(_)) == \E t \in {var} : t = var /\ Action(t)

and that works too! I guess that's because the quantification happens outside the priming, and so t is a fresh, bound symbol rather than an _expression_ involving a variable.

Thanks again!