Applies a conversion to the body of an abstraction.
If c is a conversion that maps a term tm to the theorem |- tm = tm',
then the conversion ABS_CONV c maps abstractions of the form \x.tm to
theorems of the form:
|- (\x.tm) = (\x.tm')
That is, ABS_CONV c (\x.t) applies c to the body of the
ABS_CONV c tm fails if tm is not an abstraction or if tm has the form
\x.t but the conversion c fails when applied to the term t. The
function returned by ABS_CONV c may also fail if the ML function
c:term->thm is not, in fact, a conversion (i.e. a function that maps a term
M to a theorem |- M = N).
- ABS_CONV SYM_CONV (Term `\x. 1 = x`)
> val it = |- (\x. 1 = x) = (\x. x = 1) : thm