Availability:built-in
[ISO]clause(:Head, 
?Body)True if Head can be unified with a clause head and Body 
with the corresponding clause body. Gives alternative clauses on 
backtracking. For facts, Body is unified with the atom true. 
Note that SWI-Prolog allows clause/2 
to work on both dynamic and static code.97Using clause/2 
is disallowed if either the flag iso 
or protect_static_code 
is true. Note that clause/2 decompiles 
the actual clause and may return a clause that is different from the 
source or asserted clause, i.e.,
clause/2 
only promises semantic equivalence.