An operator which commutes with all shift operators , so
for all real in a field. Any two shift-invariant operators commute.
An operator which commutes with all shift operators , so
for all real in a field. Any two shift-invariant operators commute.
Weisstein, Eric W. "Shift-Invariant Operator." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Shift-InvariantOperator.html