Dicephalic parapagus twins complete hearts are present as well, which improves their chances of survival. The total number of arms may be two, three or four. Their prospects are best if no attempt is made to separate them, except in cases where one twin is clearly dying. Dicephalus means two-headed. Parapagus means joined side by side. Dicephalic twins are called: Conjoined twins appear in one in 50,000 to one in 100,000 births. Dicephalic twins represent about 11 percent of all conjoined twins. As late as the 1960s, some medical publications argued that newborn dicephalic twins should not be actively treated or resuscitated. An
There are known knowns management and strategic planning circles. Known unknowns refers to "risks you are aware of, such as cancelled flights..." Unknown unknowns are risks that come from situations that are so unexpected that they would not be considered. "For example, prior to the invention of the personal computer, manufacturers of typewriters probably didn't foresee the risks to their business". Contemporary usage is largely consistent with the earliest known usages. For example, the term was used in evidence given to the British Columbia Royal Commission of Inquiry into Uranium Mining in 1979: The term also appeared in a 1982 "New Yorker" article on