sentences:  Don't-care term
  
  In digital logic, a don't-care term (abbreviated DC, historically also known as "redundancies", "irrelevancies", "optional entries", "invalid combinations", "vacuous combinations", "forbidden combinations", or "unused states") for a function is an input-sequence (a series of bits) for which the function output does not matter.An input that is known never to occur is a can't-happen term.