Units
lIf the first argument of reduce is an algebraic operator, then
lNormally the second argument is the unit for that operator.
lA unit has the property that for any X,
b(u,
X) = b(X, u) = X.
l0 is the unit for +, 1 is the unit for *,
[] is the unit for append.
lNormally the second argument is the unit for that operator.
lA unit has the property that for any X,
b(u,
X) = b(X, u) = X.l0 is the unit for +, 1 is the unit for *,
[] is the unit for append.