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|context> => |context: prolog example>

supported-ops |sally> => |op: mother> + |op: father>
mother |sally> => |trude>
father |sally> => |tom>

supported-ops |tom> => |op: child> + |op: father>
child |tom> => |sally> + |erica>
father |tom> => |mike>

supported-ops |erica> => |op: father>
father |erica> => |tom>

supported-ops |mike> => |op: child>
child |mike> => |tom>

supported-ops |*> => |op: parent> + |op: sibling> + |op: sibling-clean>
parent |*> #=> mother |_self> + father |_self>
sibling |*> #=> child parent |_self>
sibling-clean |*> #=> drop (child parent |_self> + -|_self>)
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