assumptions:
1 T. '' returns the last task id created.
1 T. '' gives the number of tasks extant
2 T. '' returns a list of all task ids
2 T. '' gives a list of _idle_ task ids
3 T. '' returns 0
3 T.'' gives the current task id
4 T. '' returns empty/i.0
4 T. y, for an array of pyxes y, gives a task id for a still-running pyx;
_1000 for a pyx which succeeded; a negated error code if it failed; and
_1001 if it not a pyx.
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