The Muller C-element, or Muller C-gate, is a commonly used asynchronous logic component originally designed by David E. Muller. It applies logical operations on the inputs and has hysteresis. The output of the C-element reflects the inputs when the states of all inputs match. The output then remains in this state until the inputs all transition to the other state. This model can be extended to the asymmetric C-element where some inputs only affect the operation in one of the transitions (positive or negative).
The Muller C-element was first used in the arithmetic logic unit (ALU) of the ILLIAC II supercomputer, proposed in 1958, and operational in 1962.