shift(site_ref, delta)

shift adds delta to the selected site value.

It is the most common primitive for bosonic occupancies and any model where the local basis is encoded by additive integer updates.

Example:

hopping_update = shift("i", -1).shift("j", +1)

Because updates are immutable and chainable, paired shifts are a natural way to express a hopping move. For the common occupation-transfer case, prefer the equivalent hop(src, dst, amount=1) helper.