rp: are reserved to system.
If value of such variables with no description in document are refered
or value of such variables are changed, the effect is unpreditable.
If allocation of memory necessary for rearrange heap failed, pi will terminate abnormally. If it is impassoble to estimate amount of heap usage and abnormal termination is not permitted, some consideration is required, such as doing a checkpoint dump occasionally and restart program by some external machanism (shell script, in example.)
The following problem arises in Cygwin b19.1 environment.
Char-ready? does not work properly.
The following problem arises in win32 environment if compiled with Borland C++.
(atan +i).