/* This REXX uses a lot of REXX keywords as variables. */

signal=(interpret=value);value=(interpret<parse);do upper=value to value
end;exit=upper*upper*upper*upper-value-upper;say=' ';return=say say say;
with.=signal;do then=value to exit;pull='';do otherwise=upper to then-,
value;select=otherwise-value;if.otherwise=with.otherwise+with.select;end
if.value=value;if.then=value;do otherwise=value to exit-then;pull=pull,
say''say;end;do otherwise=value to then;pull=pull center(if.otherwise,,
length(return));end;say pull;do otherwise=value to exit;with.otherwise=,
if.otherwise;end;end