Availability:C-language interface function
PL_engine_t PL_create_engine(PL_thread_attr_t 
*attributes)Create a new Prolog engine. attributes is described with
PL_thread_attach_engine(). 
Any thread can make this call after
PL_initialise() 
returns success. The returned engine is not attached to any thread and 
lives until PL_destroy_engine() 
is used on the returned handle.
In the single-threaded version this call always returns NULL, 
indicating failure.