`SUB_CONV : conv -> conv`
STRUCTURE
SYNOPSIS
Applies a conversion to the top-level subterms of a term.
DESCRIPTION
For any conversion c, the function returned by SUB_CONV c is a conversion that applies c to all the top-level subterms of a term. Its implementation is
```  fun SUB_CONV c = TRY_CONV (COMB_CONV c ORELSEC ABS_CONV c)
```
EXAMPLE
If the conversion c maps t to |- t = t', then SUB_CONV c maps an abstraction ``\x.t`` to the theorem:
```   |- (\x.t) = (\x.t')
```
That is, SUB_CONV c ``\x.t`` applies c to the body of the abstraction ``\x.t``. If c is a conversion that maps ``t1`` to the theorem |- t1 = t1' and ``t2`` to the theorem |- t2 = t2', then the conversion SUB_CONV c maps an application ``t1 t2`` to the theorem:
```   |- (t1 t2) = (t1' t2')
```
That is, SUB_CONV c ``t1 t2`` applies c to the both the operator t1 and the operand t2 of the application ``t1 t2``. Finally, for any conversion c, the function returned by SUB_CONV c acts as the identity conversion on variables and constants. That is, if ``t`` is a variable or constant, then SUB_CONV c ``t`` raises the UNCHANGED exception.
FAILURE
SUB_CONV c tm fails if tm is an abstraction ``\x.t`` and the conversion c fails when applied to t, or if tm is an application ``t1 t2`` and the conversion c fails when applied to either t1 or t2. The function returned by SUB_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 t to a theorem |- t = t').
SEEALSO